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<p><strong>Enzymes</strong> are <a title="Protein" href="http://en.wikipedia.org/wiki/Protein">proteins</a> that <a title="Catalyst" href="http://en.wikipedia.org/wiki/Catalyst">catalyze</a> (<em>i.e.</em> <a title="Reaction rate" href="http://en.wikipedia.org/wiki/Reaction_rate">accelerate</a>) <a title="Chemical reaction" href="http://en.wikipedia.org/wiki/Chemical_reaction">chemical reactions</a>. In these reactions, the <a title="Molecule" href="http://en.wikipedia.org/wiki/Molecule">molecules</a> at the beginning of the process are called <a title="Substrate (biochemistry)" href="http://en.wikipedia.org/wiki/Substrate_%28biochemistry%29">substrates</a>, and the enzyme converts them into different molecules, the products. Almost all processes in the <a title="Cell (biology)" href="http://en.wikipedia.org/wiki/Cell_%28biology%29">cell</a> need enzymes in order to occur at significant rates. Since enzymes are extremely selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which <a title="Metabolic pathway" href="http://en.wikipedia.org/wiki/Metabolic_pathway">metabolic pathways</a> occur in that cell.</p>
<p>Like all catalysts, enzymes work by lowering the <a title="Activation energy" href="http://en.wikipedia.org/wiki/Activation_energy" style="">activation energy</a> (ΔG<sup>‡</sup>) for a reaction, thus dramatically accelerating the rate of the reaction. Most enzyme reaction rates are millions of times faster than those of comparable uncatalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the <a title="Chemical equilibrium" href="http://en.wikipedia.org/wiki/Chemical_equilibrium">equilibrium</a> of these reactions. However, enzymes do differ from most other catalysts by being much more specific. Enzymes are known to catalyze about 4,000 biochemical reactions.<sup class="reference" id="_ref-0"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-0">[1]</a></sup> Not all biochemical catalysts are proteins, since some <a title="RNA" href="http://en.wikipedia.org/wiki/RNA">RNA</a> molecules called <a title="Ribozyme" href="http://en.wikipedia.org/wiki/Ribozyme">ribozymes</a> also catalyze reactions.</p>
<p>Enzyme activity can be affected by other molecules. <a title="Enzyme inhibitor" href="http://en.wikipedia.org/wiki/Enzyme_inhibitor">Inhibitors</a> are molecules that decrease enzyme activity; activators are molecules that increase activity. Many <a title="Drug" href="http://en.wikipedia.org/wiki/Drug">drugs</a> and <a title="Poison" href="http://en.wikipedia.org/wiki/Poison">poisons</a> are enzyme inhibitors. Activity is also affected by <a title="Temperature" href="http://en.wikipedia.org/wiki/Temperature">temperature</a>, <a title="PH" href="http://en.wikipedia.org/wiki/PH">pH</a>, and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of <a title="Antibiotic" href="http://en.wikipedia.org/wiki/Antibiotic">antibiotics</a>. In addition, some household products use enzymes to speed up biochemical reactions (<em>e.g.</em>, enzymes in biological washing powders break down protein or <a title="Fat" href="http://en.wikipedia.org/wiki/Fat">fat</a> stains on clothes; enzymes in meat tenderizers break down proteins, making the meat easier to chew).</p>
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<h2><span class="mw-headline">Etymology and history</span></h2>
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<div class="thumbinner" style="widthWIDTH: 177px;" ><a class="thumbinnerinternal"><a title="Eduard Buchner" class="internal" href="http://en.wikipedia.org/wiki/Image:Eduardbuchner.jpg"><img widthclass="175thumbimage" height="245" classalt="Eduard Buchner" width="thumbimage175" longdesc="/wiki/Image:Eduardbuchner.jpg" alt="Eduard Buchner" src="http://upload.wikimedia.org/wikipedia/commons/thumb/b/b2/Eduardbuchner.jpg/175px-Eduardbuchner.jpg" /></a>
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<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Eduardbuchner.jpg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
<a title="Eduard Buchner" href="http://en.wikipedia.org/wiki/Eduard_Buchner">Eduard Buchner</a></div>
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<p>As early as the late <a title="18th century" href="http://en.wikipedia.org/wiki/18th_century">1700s</a> and early <a title="19th century" href="http://en.wikipedia.org/wiki/19th_century">1800s</a>, the digestion of <a title="Meat" href="http://en.wikipedia.org/wiki/Meat">meat</a> by stomach secretions<sup class="reference" id="_ref-Reaumur1752_0"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-Reaumur1752">[2]</a></sup> and the conversion of <a title="Starch" href="http://en.wikipedia.org/wiki/Starch">starch</a> to <a title="Sugar" href="http://en.wikipedia.org/wiki/Sugar">sugars</a> by plant extracts and <a title="Saliva" href="http://en.wikipedia.org/wiki/Saliva">saliva</a> were known. However, the mechanism by which this occurred had not been identified.<sup class="reference" id="_ref-1"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-1">[3]</a></sup></p>
<p>In the 19th century, when studying the <a title="Fermentation (food)" href="http://en.wikipedia.org/wiki/Fermentation_%28food%29">fermentation</a> of sugar to <a title="Alcohol" href="http://en.wikipedia.org/wiki/Alcohol">alcohol</a> by <a title="Yeast" href="http://en.wikipedia.org/wiki/Yeast">yeast</a>, <a title="Louis Pasteur" href="http://en.wikipedia.org/wiki/Louis_Pasteur">Louis Pasteur</a> came to the conclusion that this fermentation was catalyzed by a vital force contained within the yeast cells called "<a title="Vitalism" href="http://en.wikipedia.org/wiki/Vitalism">ferments</a>", which were thought to function only within living organisms. He wrote that "alcoholic fermentation is an act correlated with the life and organisation of the yeast cells, not with the death or putrefaction of the cells."<sup class="reference" id="_ref-2"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-2">[4]</a></sup></p>
<p>In 1878 German physiologist <a title="Wilhelm Kühne" href="http://en.wikipedia.org/wiki/Wilhelm_K%C3%BChne">Wilhelm Kühne</a> (1837–1900) coined the term <em><a class="extiw" title="wiktionary:enzyme" class="extiw" href="http://en.wiktionary.org/wiki/enzyme">enzyme</a></em>, which comes from <a title="Greek language" href="http://en.wikipedia.org/wiki/Greek_language">Greek</a> <em>ενζυμον</em> "in leaven", to describe this process. The word <em>enzyme</em> was used later to refer to nonliving substances such as <a title="Pepsin" href="http://en.wikipedia.org/wiki/Pepsin">pepsin</a>, and the word <em>ferment</em> used to refer to chemical activity produced by living organisms.</p>
<p>In <a title="1897" href="http://en.wikipedia.org/wiki/1897">1897</a> <a title="Eduard Buchner" href="http://en.wikipedia.org/wiki/Eduard_Buchner">Eduard Buchner</a> began to study the ability of yeast extracts to ferment sugar despite the absence of living yeast cells. In a series of experiments at the <a title="Humboldt University of Berlin" href="http://en.wikipedia.org/wiki/Humboldt_University_of_Berlin">University of Berlin</a>, he found that the sugar was fermented even when there were no living yeast cells in the mixture.<sup class="reference" id="_ref-3"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-3">[5]</a></sup> He named the enzyme that brought about the fermentation of sucrose "<a title="Zymase" href="http://en.wikipedia.org/wiki/Zymase">zymase</a>".<sup class="reference" id="_ref-4"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-4">[6]</a></sup> In 1907 he received the <a title="Nobel Prize in Chemistry" href="http://en.wikipedia.org/wiki/Nobel_Prize_in_Chemistry">Nobel Prize in Chemistry</a> "for his biochemical research and his discovery of cell-free fermentation". Following Buchner's example; enzymes are usually named according to the reaction they carry out. Typically the suffix <em>-ase</em> is added to the name of the <a title="Substrate (biochemistry)" href="http://en.wikipedia.org/wiki/Substrate_%28biochemistry%29">substrate</a> (<em>e.g.</em>, <a title="Lactase" href="http://en.wikipedia.org/wiki/Lactase">lactase</a> is the enzyme that cleaves <a title="Lactose" href="http://en.wikipedia.org/wiki/Lactose">lactose</a>) or the type of reaction (<em>e.g.</em>, <a title="DNA polymerase" href="http://en.wikipedia.org/wiki/DNA_polymerase">DNA polymerase</a> forms DNA polymers).</p>
<p>Having shown that enzymes could function outside a living cell, the next step was to determine their biochemical nature. Many early workers noted that enzymatic activity was associated with proteins, but several scientists (such as Nobel laureate <a title="Richard Willstätter" href="http://en.wikipedia.org/wiki/Richard_Willst%C3%A4tter">Richard Willstätter</a>) argued that proteins were merely carriers for the true enzymes and that proteins <em>per se</em> were incapable of catalysis. However, in 1926, <a title="James B. Sumner" href="http://en.wikipedia.org/wiki/James_B._Sumner">James B. Sumner</a> showed that the enzyme <a title="Urease" href="http://en.wikipedia.org/wiki/Urease">urease</a> was a pure protein and crystallized it; Sumner did likewise for the enzyme <a title="Catalase" href="http://en.wikipedia.org/wiki/Catalase">catalase</a> in 1937. The conclusion that pure proteins can be enzymes was definitively proved by <a title="John Howard Northrop" href="http://en.wikipedia.org/wiki/John_Howard_Northrop">Northrop</a> and <a title="Wendell Meredith Stanley" href="http://en.wikipedia.org/wiki/Wendell_Meredith_Stanley">Stanley</a>, who worked on the digestive enzymes pepsin (1930), trypsin and chymotrypsin. These three scientists were awarded the 1946 Nobel Prize in Chemistry.<sup class="reference" id="_ref-5"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-5">[7]</a></sup></p>
<p>This discovery that enzymes could be crystalised eventually allowed their structures to be solved by <a title="X-ray crystallography" href="http://en.wikipedia.org/wiki/X-ray_crystallography">x-ray crystallography</a>. This was first done for <a title="Lysozyme" href="http://en.wikipedia.org/wiki/Lysozyme">lysozyme</a>, an enzyme found in tears, saliva and <a title="Egg white" href="http://en.wikipedia.org/wiki/Egg_white">egg whites</a> that digests the coating of some bacteria; the structure was solved by a group led by <a title="David Chilton Phillips" href="http://en.wikipedia.org/wiki/David_Chilton_Phillips">David Chilton Phillips</a> and published in 1965.<sup class="reference" id="_ref-6"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-6">[8]</a></sup> This high-resolution structure of lysozyme marked the beginning of the field of <a title="Structural biology" href="http://en.wikipedia.org/wiki/Structural_biology">structural biology</a> and the effort to understand how enzymes work at an atomic level of detail.</p>
<p><a id="Structures_and_mechanisms" name="Structures_and_mechanisms"></a></p>
<h2><span class="editsection">[<a title="Edit section: Structures and mechanisms" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=2">edit</a>]</span> <span class="mw-headline">Structures and mechanisms</span></h2>
<dl><dd><span class="boilerplate seealso"><em>See also: <a title="Enzyme catalysis" href="http://en.wikipedia.org/wiki/Enzyme_catalysis">Enzyme catalysis</a></em></span></dd></dl>
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<div class="thumbinner" style="widthWIDTH: 302px;" ><a class="thumbinnerinternal"><a title="Ribbon-diagram showing carbonic anhydrase II. The grey sphere is the zinc cofactor in the active site. Diagram drawn from PDB 1MOO." class="internal" href="http://en.wikipedia.org/wiki/Image:Carbonic_anhydrase.png"><img widthclass="300thumbimage" height="274" class="thumbimage" longdesc="/wiki/Image:Carbonic_anhydrase.png" alt="Ribbon-diagram showing carbonic anhydrase II. The grey sphere is the zinc cofactor in the active site. Diagram drawn from PDB 1MOO." width="300" longdesc="/wiki/Image:Carbonic_anhydrase.png" src="http://upload.wikimedia.org/wikipedia/en/thumb/4/40/Carbonic_anhydrase.png/300px-Carbonic_anhydrase.png" /></a>
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<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Carbonic_anhydrase.png"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>Ribbon-diagram showing <a title="Carbonic anhydrase" href="http://en.wikipedia.org/wiki/Carbonic_anhydrase">carbonic anhydrase II</a>. The grey sphere is the <a title="Zinc" href="http://en.wikipedia.org/wiki/Zinc">zinc</a> cofactor in the active site. Diagram drawn from <a relclass="nofollowexternal text" title="http://www.rcsb.org/pdb/explore.do?structureId=1MOO" classrel="external textnofollow" href="http://www.rcsb.org/pdb/explore.do?structureId=1MOO">PDB 1MOO</a>.</div>
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<p>Like all proteins, enzymes are made as long, linear chains of amino acids that <a title="Protein folding" href="http://en.wikipedia.org/wiki/Protein_folding">fold</a> to produce a <a title="Tertiary structure" href="http://en.wikipedia.org/wiki/Tertiary_structure">three-dimensional product</a>. Each unique amino acid sequence produces a unique structure, which has unique properties. Individual protein chains may sometimes group together to form a <a title="Protein complex" href="http://en.wikipedia.org/wiki/Protein_complex">protein complex</a>. Most enzymes can be <a title="Denaturation (biochemistry)" href="http://en.wikipedia.org/wiki/Denaturation_%28biochemistry%29">denatured</a>—that is, unfolded and inactivated—by heating, which destroys the <a title="Tertiary structure" href="http://en.wikipedia.org/wiki/Tertiary_structure">three-dimensional structure</a> of the protein. Depending on the enzyme, denaturation may be reversible or irreversible.</p>
<p><a id="Specificity" name="Specificity"></a></p>
<h3><span class="editsection">[<a title="Edit section: Specificity" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=3">edit</a>]</span> <span class="mw-headline">Specificity</span></h3>
<p>Enzymes are usually very specific as to which reactions they catalyze and the <a title="Substrate (biochemistry)" href="http://en.wikipedia.org/wiki/Substrate_%28biochemistry%29">substrates</a> that are involved in these reactions. Complementary shape, charge and <a title="Hydrophilic" href="http://en.wikipedia.org/wiki/Hydrophilic">hydrophilic</a>/<a title="Hydrophobic" href="http://en.wikipedia.org/wiki/Hydrophobic">hydrophobic</a> characteristics of enzymes and substrates are responsible for this specificity. Enzymes can also show impressive levels of <a title="Stereospecificity" href="http://en.wikipedia.org/wiki/Stereospecificity">stereospecificity</a>, <a title="Regioselectivity" href="http://en.wikipedia.org/wiki/Regioselectivity">regioselectivity</a> and <a title="Chemoselectivity" href="http://en.wikipedia.org/wiki/Chemoselectivity">chemoselectivity</a>.<sup class="reference" id="_ref-9"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-9">[11]</a></sup></p>
<p>Some of the enzymes showing the highest specificity and accuracy are involved in the copying and expression of the <a title="Genome" href="http://en.wikipedia.org/wiki/Genome">genome</a>. These enzymes have "proof-reading" mechanisms. Here, an enzyme such as <a title="DNA polymerase" href="http://en.wikipedia.org/wiki/DNA_polymerase">DNA polymerase</a> catalyses a reaction in a first step and then checks that the product is correct in a second step.<sup class="reference" id="_ref-10"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-10">[12]</a></sup> This two-step process results in average error rates of less than 1 error in 100 million reactions in high-fidelity mammalian polymerases.<sup class="reference" id="_ref-11"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-11">[13]</a></sup> Similar proofreading mechanisms are also found in <a title="RNA polymerase" href="http://en.wikipedia.org/wiki/RNA_polymerase">RNA polymerase</a><sup class="reference" id="_ref-12"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-12">[14]</a></sup>, <a title="Aminoacyl tRNA synthetase" href="http://en.wikipedia.org/wiki/Aminoacyl_tRNA_synthetase">aminoacyl tRNA synthetases</a><sup class="reference" id="_ref-13"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-13">[15]</a></sup> and <a title="Ribosome" href="http://en.wikipedia.org/wiki/Ribosome">ribosomes</a>.<sup class="reference" id="_ref-14"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-14">[16]</a></sup></p>
<p>Some enzymes that produce <a title="Secondary metabolite" href="http://en.wikipedia.org/wiki/Secondary_metabolite">secondary metabolites</a> are described as promiscuous, as they can act on a relatively broad range of different substrates. It has been suggested that this broad substrate specificity is important for the evolution of new biosynthetic pathways.<sup class="reference" id="_ref-15"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-15">[17]</a></sup></p>
<p><a name=".22Lock_and_key.22_model"></a></p>
<h4><span class="editsection">[<a title="Edit section: "Lock and key" model" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=4">edit</a>]</span> <span class="mw-headline">"Lock and key" model</span></h4>
<p>Enzymes are very specific, and it was suggested by <a title="Emil Fischer" href="http://en.wikipedia.org/wiki/Emil_Fischer">Emil Fischer</a> in 1894 that this was because both the enzyme and the substrate possess specific complementary geometric shapes that fit exactly into one another.<sup class="reference" id="_ref-16"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-16">[18]</a></sup> This is often referred to as "the lock and key" model. However, while this model explains enzyme specificity, it fails to explain the stabilization of the transition state that enzymes achieve.</p>
<p><a id="Induced_fit_model" name="Induced_fit_model"></a></p>
<h4><span class="editsection">[<a title="Edit section: Induced fit model" href="http://en.wikipedia.org/w/index.php?title=Enzyme&nbsp;action=edit&section=5">edit</a>]</span> <span class="mw-headline">Induced fit model</span></h4>
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<div class="thumbinner" style="widthWIDTH: 452px;" ><a class="thumbinnerinternal"><a title="Diagrams to show the induced fit hypothesis of enzyme action." class="internal" href="http://en.wikipedia.org/wiki/Image:Induced_fit_diagram.svg"><img widthclass="450thumbimage" height="176" classalt="Diagrams to show the induced fit hypothesis of enzyme action." width="thumbimage450" longdesc="/wiki/Image:Induced_fit_diagram.svg" alt="Diagrams to show the induced fit hypothesis of enzyme action." src="http://upload.wikimedia.org/wikipedia/commons/thumb/2/24/Induced_fit_diagram.svg/450px-Induced_fit_diagram.svg.png" /></a>
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<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Induced_fit_diagram.svg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Diagrams to show the induced fit hypothesis of enzyme action.</div>
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<p>In 1958 <a class="new" title="Daniel Koshland" class="new" href="http://en.wikipedia.org/w/index.php?title=Daniel_Koshland&action=edit">Daniel Koshland</a> suggested a modification to the lock and key model: since enzymes are rather flexible structures, the active site can be reshaped by interactions with the substrate as the substrate interacts with the enzyme.<sup class="reference" id="_ref-17"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-17">[19]</a></sup> As a result, the amino acid <a title="Side chain" href="http://en.wikipedia.org/wiki/Side_chain">side chains</a> which make up the active site are molded into the precise positions that enable the enzyme to perform its catalytic function. In some cases, such as glycosidases, the substrate molecule also changes shape slightly as it enters the active site.<sup class="reference" id="_ref-18"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-18">[20]</a></sup></p>
<p><a id="Mechanisms" name="Mechanisms"></a></p>
<h3><span class="editsection">[<a title="Edit section: Mechanisms" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=6">edit</a>]</span> <span class="mw-headline">Mechanisms</span></h3>
<p>Enzymes can act in several ways, all of which lower ΔG<sup>‡</sup>:<sup class="reference" id="_ref-19"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-19">[21]</a></sup></p>
<ul>
<li>Lowering the <a title="Activation energy" href="http://en.wikipedia.org/wiki/Activation_energy">activation energy</a> by creating an environment in which the transition state is stabilised (e.g. straining the shape of a substrate - by binding the transition-state conformation of the substrate/product molecules, the enzyme distorts the bound substrate(s) into their transition state form, thereby reducing the amount of energy required to complete the transition).</li>
</ul>
<ul>
<li>Providing an alternative pathway (e.g. temporarily reacting with the substrate to form an intermediate which would be impossible in the absence of the enzyme).</li>
</ul>
<ul>
<li>Reducing the reaction entropy change by bringing substrates together in the correct orientation to react. Considering ΔH<sup>‡</sup> alone overlooks this effect.</li>
</ul>
<p><a id="Dynamics_and_function" name="Dynamics_and_function"></a></p>
<h4><span class="editsection">[<a title="Edit section: Dynamics and function" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=7">edit</a>]</span> <span class="mw-headline">Dynamics and function</span></h4>
<p>Recent investigations have provided new insights into the connection between internal dynamics of enzymes and their mechanism of catalysis.<sup class="reference" id="_ref-20"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-20">[22]</a></sup><sup class="reference" id="_ref-21"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-21">[23]</a></sup><sup class="reference" id="_ref-22"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-22">[24]</a></sup> An enzyme's internal dynamics are described as the movement of internal parts (<em>e.g.</em> amino acids, a group of amino acids, a loop region, an alpha helix, neighboring beta-sheets or even entire domain) of these biomolecules, which can occur at various time-scales ranging from <a title="Femtoseconds" href="http://en.wikipedia.org/wiki/Femtoseconds">femtoseconds</a> to seconds. Networks of protein residues throughout an enzyme's structure can contribute to catalysis through dynamic motions.<sup class="reference" id="_ref-23"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-23">[25]</a></sup><sup class="reference" id="_ref-24"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-24">[26]</a></sup><sup class="reference" id="_ref-25"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-25">[27]</a></sup><sup class="reference" id="_ref-26"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-26">[28]</a></sup> Protein motions are vital to many enzymes, but whether small and fast vibrations or larger and slower conformational movements are more important depends on the type of reaction involved. These new insights also have implications in understanding allosteric effects, producing designer enzymes and developing new drugs.</p>
<p><a id="Allosteric_modulation" name="Allosteric_modulation"></a></p>
<h3><span class="editsection">[<a title="Edit section: Allosteric modulation" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=8">edit</a>]</span> <span class="mw-headline">Allosteric modulation</span></h3>
<p><a title="Allosteric" href="http://en.wikipedia.org/wiki/Allosteric">Allosteric</a> enzymes change their structure in response to binding of <a title="Effector (biology)" href="http://en.wikipedia.org/wiki/Effector_%28biology%29">effectors</a>. Modulation can be direct, where the effector binds directly to <a title="Binding site" href="http://en.wikipedia.org/wiki/Binding_site">binding sites</a> in the enzyme, or indirect, where the effector binds to other proteins or <a title="Protein subunit" href="http://en.wikipedia.org/wiki/Protein_subunit">protein subunits</a> that interact with the allosteric enzyme and thus influence catalytic activity.</p>
<p><a id="Cofactors_and_coenzymes" name="Cofactors_and_coenzymes"></a></p>
<h2><span class="editsection">[<a title="Edit section: Cofactors and coenzymes" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=9">edit</a>]</span> <span class="mw-headline">Cofactors and coenzymes</span></h2>
<dl><dd>
<div class="noprint"><em>Main articles: <a title="Cofactor (biochemistry)" href="http://en.wikipedia.org/wiki/Cofactor_%28biochemistry%29">Cofactor (biochemistry)</a> and <a title="Coenzyme" href="http://en.wikipedia.org/wiki/Coenzyme">Coenzyme</a></em></div>
</dd></dl>
<p><a id="Cofactors" name="Cofactors"></a></p>
<h3><span class="editsection">[<a title="Edit section: Cofactors" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=10">edit</a>]</span> <span class="mw-headline">Cofactors</span></h3>
<p>Some enzymes do not need any additional components to show full activity. However, others require non-protein molecules to be bound for activity. Cofactors can be either <a title="Inorganic" href="http://en.wikipedia.org/wiki/Inorganic">inorganic</a> (<em>e.g.</em>, metal ions and <a title="Iron-sulfur cluster" href="http://en.wikipedia.org/wiki/Iron-sulfur_cluster">iron-sulfur clusters</a>) or <a title="Organic molecules" href="http://en.wikipedia.org/wiki/Organic_molecules">organic compounds</a>, (e.g., <a title="Flavin" href="http://en.wikipedia.org/wiki/Flavin">flavin</a> and <a title="Heme" href="http://en.wikipedia.org/wiki/Heme">heme</a>). Organic cofactors (coenzymes) are usually <a title="Prosthetic groups" href="http://en.wikipedia.org/wiki/Prosthetic_groups">prosthetic groups</a>, which are tightly bound to the enzymes that they assist. These tightly-bound cofactors are distinguished from other coenzymes, such as <a title="Nicotinamide adenine dinucleotide" href="http://en.wikipedia.org/wiki/Nicotinamide_adenine_dinucleotide">NADH</a>, since they are not released from the active site during the reaction.</p>
<p>An example of an enzyme that contains a cofactor is <a title="Carbonic anhydrase" href="http://en.wikipedia.org/wiki/Carbonic_anhydrase">carbonic anhydrase</a>, and is shown in the ribbon diagram above with a zinc cofactor bound in its active site.<sup class="reference" id="_ref-27"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-27">[29]</a></sup> These tightly-bound molecules are usually found in the active site and are involved in catalysis. For example, flavin and heme cofactors are often involved in <a title="Redox" href="http://en.wikipedia.org/wiki/Redox">redox</a> reactions.</p>
<p>Enzymes that require a cofactor but do not have one bound are called apoenzymes. An apoenzyme together with its cofactor(s) is called a holoenzyme (<em>i.e.</em>, the active form). Most cofactors are not covalently attached to an enzyme, but are very tightly bound. However, organic prosthetic groups can be covalently bound (<em>e.g.</em>, <a title="Thiamine pyrophosphate" href="http://en.wikipedia.org/wiki/Thiamine_pyrophosphate">thiamine pyrophosphate</a> in the enzyme <a title="Pyruvate dehydrogenase" href="http://en.wikipedia.org/wiki/Pyruvate_dehydrogenase">pyruvate dehydrogenase</a>).</p>
<p><a id="Coenzymes" name="Coenzymes"></a></p>
<h3><span class="editsection">[<a title="Edit section: Coenzymes" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=11">edit</a>]</span> <span class="mw-headline">Coenzymes</span></h3>
<div class="thumb tleft">
<div class="thumbinner" style="widthWIDTH: 152px;" ><a class="thumbinnerinternal"><a title="Space-filling model of the coenzyme NADH" class="internal" href="http://en.wikipedia.org/wiki/Image:NADH-3D-vdW.png"><img widthclass="150thumbimage" height="167" classalt="Space-filling model of the coenzyme NADH" width="thumbimage150" longdesc="/wiki/Image:NADH-3D-vdW.png" alt="Space-filling model of the coenzyme NADH" src="http://upload.wikimedia.org/wikipedia/commons/thumb/e/ed/NADH-3D-vdW.png/150px-NADH-3D-vdW.png" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:NADH-3D-vdW.png"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
<a title="Molecular graphics" href="http://en.wikipedia.org/wiki/Molecular_graphics#Space-filling_models">Space-filling model</a> of the coenzyme NADH</div>
</div>
<p>Coenzymes are usually regenerated and their concentrations maintained at a steady level inside the cell: for example, NADPH is regenerated through the <a title="Pentose phosphate pathway" href="http://en.wikipedia.org/wiki/Pentose_phosphate_pathway">pentose phosphate pathway</a> and <em>S</em>-adenosylmethionine by methionine adenosyltransferase.</p>
<p><a id="Thermodynamics" name="Thermodynamics"></a></p>
<h2><span class="editsection">[<a title="Edit section: Thermodynamics" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=12">edit</a>]</span> <span class="mw-headline">Thermodynamics</span></h2>
<dl><dd>
<div class="noprint"><em>Main articles: <a title="Activation energy" href="http://en.wikipedia.org/wiki/Activation_energy">Activation energy</a>, <a title="Thermodynamic equilibrium" href="http://en.wikipedia.org/wiki/Thermodynamic_equilibrium">Thermodynamic equilibrium</a>, and <a title="Chemical equilibrium" href="http://en.wikipedia.org/wiki/Chemical_equilibrium">Chemical equilibrium</a></em></div>
</dd></dl>
<div class="thumb tright">
<div class="thumbinner" style="widthWIDTH: 302px;" ><a class="thumbinnerinternal"><a title="Diagram of a catalytic reaction, showing the energy niveau at each stage of the reaction. The substrates usually need a large amount of energy to reach the transition state, which then decays into the end product. The enzyme stabilizes the transition state, reducing the energy needed to form this species and thus reducing the energy required to form products." class="internal" href="http://en.wikipedia.org/wiki/Image:Activation2_updated.svg"><img widthclass="300thumbimage" height="235" class="thumbimage" longdesc="/wiki/Image:Activation2_updated.svg" alt="Diagram of a catalytic reaction, showing the energy niveau at each stage of the reaction. The substrates usually need a large amount of energy to reach the transition state, which then decays into the end product. The enzyme stabilizes the transition state, reducing the energy needed to form this species and thus reducing the energy required to form products." width="300" longdesc="/wiki/Image:Activation2_updated.svg" src="http://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/Activation2_updated.svg/300px-Activation2_updated.svg.png" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Activation2_updated.svg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Diagram of a catalytic reaction, showing the energy <em>niveau</em> at each stage of the reaction. The substrates usually need a large amount of energy to reach the transition state, which then decays into the end product. The enzyme stabilizes the transition state, reducing the energy needed to form this species and thus reducing the energy required to form products.</div>
</div>
<p>Furthermore, enzymes can couple two or more reactions, so that a thermodynamically favorable reaction can be used to "drive" a thermodynamically unfavorable one. For example, the hydrolysis of <a title="Adenosine triphosphate" href="http://en.wikipedia.org/wiki/Adenosine_triphosphate">ATP</a> is often used to drive other chemical reactions.</p>
<p>Enzymes catalyze the forward and backward reactions equally. They do not alter the equilibrium itself, but only the speed at which it is reached. For example, <a title="Carbonic anhydrase" href="http://en.wikipedia.org/wiki/Carbonic_anhydrase">carbonic anhydrase</a> catalyzes its reaction in either direction depending on the concentration of its reactants.</p>
<dl><dd><img class="tex" alt="\mathrm{CO_2 + H_2O {}^\mathrm{\quad Carbonic\ anhydrase} \!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\! \overrightarrow{\qquad\qquad\qquad\qquad} H_2CO_3}" src="http://upload.wikimedia.org/math/c/8/c/c8c255d26e3f46da6bbacb1606142e6f.png" class="tex" /> (in <a title="Biological tissue" href="http://en.wikipedia.org/wiki/Biological_tissue">tissues</a>; high CO<sub>2</sub> concentration)</dd><dd><img class="tex" alt="\mathrm{H_2CO_3 {}^\mathrm{\quad Carbonic\ anhydrase} \!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\!\! \overrightarrow{\qquad\qquad\qquad\qquad} CO_2 + H_2O}" src="http://upload.wikimedia.org/math/7/e/2/7e2012023ac3500d9e061834ffc2074e.png" class="tex" /> (in <a title="Lung" href="http://en.wikipedia.org/wiki/Lung">lungs</a>; low CO<sub>2</sub> concentration)</dd></dl>
<p>Nevertheless, if the equilibrium is greatly displaced in one direction, that is, in a very <a title="Exergonic" href="http://en.wikipedia.org/wiki/Exergonic">exergonic</a> reaction, the reaction is <em>effectively</em> irreversible. Under these conditions the enzyme will, in fact, only catalyze the reaction in the thermodynamically allowed direction.</p>
<p><a id="Kinetics" name="Kinetics"></a></p>
<h2><span class="editsection">[<a title="Edit section: Kinetics" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=13">edit</a>]</span> <span class="mw-headline">Kinetics</span></h2>
<dl><dd>
<div class="noprint"><em>Main article: <a title="Enzyme kinetics" href="http://en.wikipedia.org/wiki/Enzyme_kinetics">Enzyme kinetics</a></em></div>
</dd></dl>
<div class="thumb tleft">
<div class="thumbinner" style="widthWIDTH: 302px;" ><a class="thumbinnerinternal"><a title="Mechanism for a single substrate enzyme catalyzed reaction. The enzyme (E) binds a substrate (S) and produces a product (P)." class="internal" href="http://en.wikipedia.org/wiki/Image:Simple_mechanism.svg"><img widthclass="300thumbimage" height="117" class="thumbimage" longdesc="/wiki/Image:Simple_mechanism.svg" alt="Mechanism for a single substrate enzyme catalyzed reaction. The enzyme (E) binds a substrate (S) and produces a product (P)." width="300" longdesc="/wiki/Image:Simple_mechanism.svg" src="http://upload.wikimedia.org/wikipedia/en/thumb/9/96/Simple_mechanism.svg/300px-Simple_mechanism.svg.png" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Simple_mechanism.svg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Mechanism for a single substrate enzyme catalyzed reaction. The enzyme (E) binds a substrate (S) and produces a product (P).</div>
</div>
<p>The major contribution of Michaelis and Menten was to think of enzyme reactions in two stages. In the first, the substrate binds reversibly to the enzyme, forming the enzyme-substrate complex. This is sometimes called the Michaelis-Menten complex in their honor. The enzyme then catalyzes the chemical step in the reaction and releases the product.</p>
<div class="thumb tright">
<div class="thumbinner" style="widthWIDTH: 302px;" ><a class="thumbinnerinternal"><a title="Saturation curve for an enzyme reaction showing the relation between the substrate concentration (S) and rate (v)." class="internal" href="http://en.wikipedia.org/wiki/Image:MM_curve.png"><img widthclass="300thumbimage" height="229" class="thumbimage" longdesc="/wiki/Image:MM_curve.png" alt="Saturation curve for an enzyme reaction showing the relation between the substrate concentration (S) and rate (v)." width="300" longdesc="/wiki/Image:MM_curve.png" src="http://upload.wikimedia.org/wikipedia/commons/thumb/2/26/MM_curve.png/300px-MM_curve.png" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:MM_curve.png"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Saturation curve for an enzyme reaction showing the relation between the substrate concentration (S) and rate (<em>v</em>).</div>
</div>
<p>Some enzymes operate with kinetics which are faster than diffusion rates, which would seem to be impossible. Several mechanisms have been invoked to explain this phenomenon. Some proteins are believed to accelerate catalysis by drawing their substrate in and pre-orienting them by using dipolar electric fields. Other models invoke a quantum-mechanical <a title="Quantum tunneling" href="http://en.wikipedia.org/wiki/Quantum_tunneling">tunneling</a> explanation, whereby a proton or an electron can tunnel through activation barriers, although for proton tunneling this model remains somewhat controversial.<sup class="reference" id="_ref-33"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-33">[35]</a></sup><sup class="reference" id="_ref-34"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-34">[36]</a></sup> Quantum tunneling for protons has been observed in <a title="Tryptamine" href="http://en.wikipedia.org/wiki/Tryptamine">tryptamine</a>.<sup class="reference" id="_ref-35"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-35">[37]</a></sup> This suggests that enzyme catalysis may be more accurately characterized as "through the barrier" rather than the traditional model, which requires substrates to go "over" a lowered energy barrier.</p>
<p><a id="Inhibition" name="Inhibition"></a></p>
<h2><span class="editsection">[<a title="Edit section: Inhibition" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=14">edit</a>]</span> <span class="mw-headline">Inhibition</span></h2>
<div class="thumb tright">
<div class="thumbinner" style="widthWIDTH: 402px;" ><a class="thumbinnerinternal"><a title="Competitive inhibitors bind reversibly to the enzyme, preventing the binding of substrate. On the other hand, binding of substrate prevents binding of the inhibitor. Substrate and inhibitor compete for the enzyme." class="internal" href="http://en.wikipedia.org/wiki/Image:Competitive_inhibition.svg"><img widthclass="400thumbimage" height="280" class="thumbimage" longdesc="/wiki/Image:Competitive_inhibition.svg" alt="Competitive inhibitors bind reversibly to the enzyme, preventing the binding of substrate. On the other hand, binding of substrate prevents binding of the inhibitor. Substrate and inhibitor compete for the enzyme." width="400" longdesc="/wiki/Image:Competitive_inhibition.svg" src="http://upload.wikimedia.org/wikipedia/commons/thumb/f/fe/Competitive_inhibition.svg/400px-Competitive_inhibition.svg.png" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Competitive_inhibition.svg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Competitive inhibitors bind reversibly to the enzyme, preventing the binding of substrate. On the other hand, binding of substrate prevents binding of the inhibitor. Substrate and inhibitor compete for the enzyme.</div>
</div>
<p>Enzyme reaction rates can be decreased by various types of <a title="Enzyme inhibitor" href="http://en.wikipedia.org/wiki/Enzyme_inhibitor">enzyme inhibitors</a>.</p>
<p><a id="Reversible_inhibitors" name="Reversible_inhibitors"></a></p>
<h3><span class="editsection">[<a title="Edit section: Reversible inhibitors" href="http://en.wikipedia.org/w/index.php?title=Enzyme&nbsp;action=edit&section=15">edit</a>]</span> <span class="mw-headline">Reversible inhibitors</span></h3>
<p><strong>Competitive inhibition</strong></p>
<p>In competitive inhibition the inhibitor binds to the substrate binding site (figure <em>right</em>, top, thus preventing substrate from binding (EI complex). Often competitive inhibitors strongly resemble the real substrate of the enzyme. For example, <a title="Methotrexate" href="http://en.wikipedia.org/wiki/Methotrexate">methotrexate</a> is a competitive inhibitor of the enzyme <a title="Dihydrofolate reductase" href="http://en.wikipedia.org/wiki/Dihydrofolate_reductase">dihydrofolate reductase</a>, which catalyzes the reduction of <a title="Folic acid" href="http://en.wikipedia.org/wiki/Folic_acid">dihydrofolate</a> to <a title="Folic acid" href="http://en.wikipedia.org/wiki/Folic_acid">tetrahydrofolate</a>. The similarity between the structures of folic acid and this drug are shown in the figure to the <em>right</em> bottom.</p>
<p>Some enzyme inhibitors react with the enzyme and form a <a title="Covalent bond" href="http://en.wikipedia.org/wiki/Covalent_bond">covalent</a> adduct with the protein. The inactivation produced by this type of inhibitor cannot be reversed. A class of these compounds called <a title="Suicide inhibitor" href="http://en.wikipedia.org/wiki/Suicide_inhibitor">suicide inhibitors</a> includes <a title="Eflornithine" href="http://en.wikipedia.org/wiki/Eflornithine">eflornithine</a> a drug used to treat the parasitic disease <a title="Sleeping sickness" href="http://en.wikipedia.org/wiki/Sleeping_sickness">sleeping sickness</a>.</p>
<div class="thumb tright">
<div class="thumbinner" style="widthWIDTH: 402px;" ><a class="thumbinnerinternal"><a title="The coenzyme folic acid (left) and the anti-cancer drug methotrexate (right) are very similar in structure. As a result, methotrexate is a competitive inhibitor of many enzymes that use folates." class="internal" href="http://en.wikipedia.org/wiki/Image:Methotrexate_and_folic_acid_compared.png"><img widthclass="400thumbimage" height="128" class="thumbimage" longdesc="/wiki/Image:Methotrexate_and_folic_acid_compared.png" alt="The coenzyme folic acid (left) and the anti-cancer drug methotrexate (right) are very similar in structure. As a result, methotrexate is a competitive inhibitor of many enzymes that use folates." width="400" longdesc="/wiki/Image:Methotrexate_and_folic_acid_compared.png" src="http://upload.wikimedia.org/wikipedia/en/6/67/Methotrexate_and_folic_acid_compared.png" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Methotrexate_and_folic_acid_compared.png"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
The coenzyme folic acid (left) and the anti-cancer drug methotrexate (right) are very similar in structure. As a result, methotrexate is a competitive inhibitor of many enzymes that use folates.</div>
</div>
<h2><span class="editsection">[<a title="Edit section: Biological function" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=18">edit</a>]</span> <span class="mw-headline">Biological function</span></h2>
<p>Enzymes serve a wide variety of functions inside living organisms. They are indispensable for <a title="Signal transduction" href="http://en.wikipedia.org/wiki/Signal_transduction">signal transduction</a> and cell regulation, often via <a title="Kinase" href="http://en.wikipedia.org/wiki/Kinase">kinases</a> and <a title="Phosphatase" href="http://en.wikipedia.org/wiki/Phosphatase">phosphatases</a>.<sup class="reference" id="_ref-38"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-38">[40]</a></sup> They also generate movement, with <a title="Myosin" href="http://en.wikipedia.org/wiki/Myosin">myosin</a> hydrolysing ATP to generate <a title="Muscle contraction" href="http://en.wikipedia.org/wiki/Muscle_contraction">muscle contraction</a> and also moving cargo around the cell as part of the <a title="Cytoskeleton" href="http://en.wikipedia.org/wiki/Cytoskeleton">cytoskeleton</a>.<sup class="reference" id="_ref-39"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-39">[41]</a></sup> Other ATPases in the cell membrane are <a title="Ion pump (biology)" href="http://en.wikipedia.org/wiki/Ion_pump_%28biology%29">ion pumps</a> involved in <a title="Active transport" href="http://en.wikipedia.org/wiki/Active_transport">active transport</a>. Enzymes are also involved in more exotic functions, such as <a title="Luciferase" href="http://en.wikipedia.org/wiki/Luciferase">luciferase</a> generating light in <a title="Firefly" href="http://en.wikipedia.org/wiki/Firefly">fireflies</a>.<sup class="reference" id="_ref-40"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-40">[42]</a></sup></p>
<p><a title="Virus" href="http://en.wikipedia.org/wiki/Virus">Viruses</a> can contain enzymes for infecting cells, such as the <a class="new" title="HIV integrase" class="new" href="http://en.wikipedia.org/w/index.php?title=HIV_integrase&action=edit">HIV integrase</a> and <a title="Reverse transcriptase" href="http://en.wikipedia.org/wiki/Reverse_transcriptase">reverse transcriptase</a>, or for viral release from cells, like the <a title="Influenza" href="http://en.wikipedia.org/wiki/Influenza">influenza</a> virus <a title="Neuraminidase" href="http://en.wikipedia.org/wiki/Neuraminidase">neuraminidase</a>.</p>
<p>An important function of enzymes is in the <a title="Digestive systems" href="http://en.wikipedia.org/wiki/Digestive_systems">digestive systems</a> of animals. Enzymes such as <a title="Amylases" href="http://en.wikipedia.org/wiki/Amylases">amylases</a> and <a title="Proteases" href="http://en.wikipedia.org/wiki/Proteases">proteases</a> break down large molecules (<a title="Starch" href="http://en.wikipedia.org/wiki/Starch">starch</a> or <a title="Protein" href="http://en.wikipedia.org/wiki/Protein">proteins</a>, respectively) into smaller ones, so they can be absorbed by the intestines. Starch is inabsorbable in the intestine but enzymes hydrolyse the starch chains into smaller molecules such as <a title="Maltose" href="http://en.wikipedia.org/wiki/Maltose">maltose</a> and eventually <a title="Glucose" href="http://en.wikipedia.org/wiki/Glucose">glucose</a>, which can then be absorbed. Different enzymes digest different food substances. In <a title="Ruminants" href="http://en.wikipedia.org/wiki/Ruminants">ruminants</a> which have a <a title="Herbivorous" href="http://en.wikipedia.org/wiki/Herbivorous">herbivorous</a> diets, bacteria in the gut produce another enzyme, <a title="Cellulase" href="http://en.wikipedia.org/wiki/Cellulase">cellulase</a> to break down the cellulose cell walls of plant fiber.</p>
<p>Several enzymes can work together in a specific order, creating <a title="Metabolic pathway" href="http://en.wikipedia.org/wiki/Metabolic_pathway">metabolic pathways</a>. In a metabolic pathway, one enzyme takes the product of another enzyme as a substrate. After the catalytic reaction, the product is then passed on to another enzyme. Sometimes more than one enzyme can catalyse the same reaction in parallel, this can allow more complex regulation: with for example a low contant activity being provided by one enzyme but an inducible high activity from a second enzyme.</p>
<p>There are five main ways that enzyme activity is controlled in the cell.</p>
<ol>
<li>Enzyme production (<a title="Transcription (genetics)" href="http://en.wikipedia.org/wiki/Transcription_%28genetics%29">transcription</a> and <a title="Translation (genetics)" href="http://en.wikipedia.org/wiki/Translation_%28genetics%29">translation</a> of enzyme genes) can be enhanced or diminished by a cell in response to changes in the cell's environment. This form of <a title="Regulation of gene expression" href="http://en.wikipedia.org/wiki/Regulation_of_gene_expression">gene regulation</a> is called <a title="Enzyme induction and inhibition" href="http://en.wikipedia.org/wiki/Enzyme_induction_and_inhibition">enzyme induction and inhibition</a>. For example, bacteria may become <a title="Antibiotic resistance" href="http://en.wikipedia.org/wiki/Antibiotic_resistance">resistant to antibiotics</a> such as <a title="Penicillin" href="http://en.wikipedia.org/wiki/Penicillin">penicillin</a> because enzymes called <a title="Beta-lactamase" href="http://en.wikipedia.org/wiki/Beta-lactamase">beta-lactamases</a> are induced that hydrolyse the crucial <a title="Beta-lactam" href="http://en.wikipedia.org/wiki/Beta-lactam">beta-lactam ring</a> within the penicillin molecule. Another example are enzymes in the <a title="Liver" href="http://en.wikipedia.org/wiki/Liver">liver</a> called <a title="Cytochrome P450 oxidase" href="http://en.wikipedia.org/wiki/Cytochrome_P450_oxidase">cytochrome P450 oxidases</a>, which are important in <a title="Drug metabolism" href="http://en.wikipedia.org/wiki/Drug_metabolism">drug metabolism</a>. Induction or inhibition of these enzymes can cause <a title="Drug interaction" href="http://en.wikipedia.org/wiki/Drug_interaction">drug interactions</a>.</li> <li>Enzymes can be compartmentalized, with different metabolic pathways occurring in different <a title="Cellular compartment" href="http://en.wikipedia.org/wiki/Cellular_compartment">cellular compartments</a>. For example, <a title="Fatty acids" href="http://en.wikipedia.org/wiki/Fatty_acids">fatty acids</a> are synthesized by one set of enzymes in the <a title="Cytosol" href="http://en.wikipedia.org/wiki/Cytosol">cytosol</a>, <a title="Endoplasmic reticulum" href="http://en.wikipedia.org/wiki/Endoplasmic_reticulum">endoplasmic reticulum</a> and the <a title="Golgi apparatus" href="http://en.wikipedia.org/wiki/Golgi_apparatus">Golgi apparatus</a> and used by a different set of enzymes as a source of energy in the <a title="Mitochondrion" href="http://en.wikipedia.org/wiki/Mitochondrion">mitochondrion</a>, through <a title="Β-oxidation" href="http://en.wikipedia.org/wiki/%CE%92-oxidation">β-oxidation</a>.<sup class="reference" id="_ref-41"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-41">[43]</a></sup></li> <li>Enzymes can be regulated by <a title="Enzyme inhibitor" href="http://en.wikipedia.org/wiki/Enzyme_inhibitor">inhibitors</a> and activators. For example, the end product(s) of a metabolic pathway are often inhibitors for one of the first enzymes of the pathway (usually the first irreversible step, called <em>committed step</em>), thus regulating the amount of end product made by the pathways. Such a regulatory mechanism is called a <a title="Negative feedback" href="http://en.wikipedia.org/wiki/Negative_feedback">negative feedback mechanism</a>, because the amount of the end product produced is regulated by its own concentration. Negative feedback mechanism can effectively adjust the rate of synthesis of intermediate metabolites according to the demands of the cells. This helps allocate materials and energy economically, and prevents the manufacture of excess end products. Like other <a title="Homeostasis" href="http://en.wikipedia.org/wiki/Homeostasis">homeostatic devices</a>, the control of enzymatic action helps to maintain a stable internal environment in living organisms.</li> <li>Enzymes can be regulated through <a title="Post-translational modification" href="http://en.wikipedia.org/wiki/Post-translational_modification">post-translational modification</a>. This can include <a title="Phosphorylation" href="http://en.wikipedia.org/wiki/Phosphorylation">phosphorylation</a>, <a title="Myristic acid" href="http://en.wikipedia.org/wiki/Myristic_acid">myristoylation</a> and <a title="Glycosylation" href="http://en.wikipedia.org/wiki/Glycosylation">glycosylation</a>. For example, in the response to <a title="Insulin" href="http://en.wikipedia.org/wiki/Insulin">insulin</a>, the <a title="Phosphorylation" href="http://en.wikipedia.org/wiki/Phosphorylation">phosphorylation</a> of multiple enzymes, including <a title="Glycogen synthase" href="http://en.wikipedia.org/wiki/Glycogen_synthase">glycogen synthase</a>, helps control the synthesis or degradation of <a title="Glycogen" href="http://en.wikipedia.org/wiki/Glycogen">glycogen</a> and allows the cell to respond to changes in <a title="Blood sugar" href="http://en.wikipedia.org/wiki/Blood_sugar">blood sugar</a>.<sup class="reference" id="_ref-42"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-42">[44]</a></sup> Another example of post-translational modification is the cleavage of the polypeptide chain. <a title="Chymotrypsin" href="http://en.wikipedia.org/wiki/Chymotrypsin">Chymotrypsin</a>, a digestive <a title="Protease" href="http://en.wikipedia.org/wiki/Protease">protease</a>, is produced in inactive form as <a title="Chymotrypsinogen" href="http://en.wikipedia.org/wiki/Chymotrypsinogen">chymotrypsinogen</a> in the <a title="Pancreas" href="http://en.wikipedia.org/wiki/Pancreas">pancreas</a> and transported in this form to the <a title="Stomach" href="http://en.wikipedia.org/wiki/Stomach">stomach</a> where it is activated. This stops the enzyme from digesting the pancreas or other tissues before it enters the gut. This type of inactive precursor to an enzyme is known as a <a title="Zymogen" href="http://en.wikipedia.org/wiki/Zymogen">zymogen</a>.</li> <li>Some enzymes may become activated when localized to a different environment (eg. from a reducing (<a title="Cytoplasm" href="http://en.wikipedia.org/wiki/Cytoplasm">cytoplasm</a>) to an oxidising (<a title="Periplasm" href="http://en.wikipedia.org/wiki/Periplasm">periplasm</a>) environment, high pH to low pH etc). For example, <a title="Hemagglutinin" href="http://en.wikipedia.org/wiki/Hemagglutinin">hemagglutinin</a> of the <a title="Influenza" href="http://en.wikipedia.org/wiki/Influenza">influenza</a> virus undergoes a conformational change once it encounters the acidic environment of the host cell <a title="Vesicle (biology)" href="http://en.wikipedia.org/wiki/Vesicle_%28biology%29">vesicle</a> causing its activation. <sup class="reference" id="_ref-43"><a title="" href="http://en.wikipedia.org/wiki/Enzyme#_note-43">[45]</a></sup></li>
</ol>
<p><a id="Involvement_in_disease" name="Involvement_in_disease"></a></p>
<h2><span class="editsection">[<a title="Edit section: Involvement in disease" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=20">edit</a>]</span> <span class="mw-headline">Involvement in disease</span></h2>
<div class="thumb tright">
<div class="thumbinner" style="widthWIDTH: 202px;" ><a class="thumbinnerinternal"><a title="Phenylalanine hydroxylase. Created from PDB 1KW0 " class="internal" href="http://en.wikipedia.org/wiki/Image:Phenylalanine_hydroxylase_brighter.jpg"><img widthclass="200thumbimage" height="210" classalt="Phenylalanine hydroxylase. Created from PDB 1KW0 " width="thumbimage200" longdesc="/wiki/Image:Phenylalanine_hydroxylase_brighter.jpg" alt="Phenylalanine hydroxylase. Created from PDB 1KW0 " src="http://upload.wikimedia.org/wikipedia/commons/thumb/9/97/Phenylalanine_hydroxylase_brighter.jpg/200px-Phenylalanine_hydroxylase_brighter.jpg" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Phenylalanine_hydroxylase_brighter.jpg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div><a title="Phenylalanine hydroxylase" href="http://en.wikipedia.org/wiki/Phenylalanine_hydroxylase">Phenylalanine hydroxylase</a>. Created from <a relclass="nofollowexternal text" title="http://www.rcsb.org/pdb/explore.do?structureId=1KW0" classrel="external textnofollow" href="http://www.rcsb.org/pdb/explore.do?structureId=1KW0">PDB 1KW0</a></div>
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</div>
<p>The top-level classification is</p>
<ul>
<li>EC 1 <em><a title="Oxidoreductase" href="http://en.wikipedia.org/wiki/Oxidoreductase">Oxidoreductases</a></em>: catalyze <a title="Oxidation" href="http://en.wikipedia.org/wiki/Oxidation">oxidation</a>/reduction reactions</li> <li>EC 2 <em><a title="Transferase" href="http://en.wikipedia.org/wiki/Transferase">Transferases</a></em>: transfer a <a title="Functional group" href="http://en.wikipedia.org/wiki/Functional_group">functional group</a> (<em>e.g.</em> a methyl or phosphate group)</li> <li>EC 3 <em><a title="Hydrolase" href="http://en.wikipedia.org/wiki/Hydrolase">Hydrolases</a></em>: catalyze the <a title="Hydrolysis" href="http://en.wikipedia.org/wiki/Hydrolysis">hydrolysis</a> of various bonds</li> <li>EC 4 <em><a title="Lyase" href="http://en.wikipedia.org/wiki/Lyase">Lyases</a></em>: cleave various bonds by means other than hydrolysis and oxidation</li> <li>EC 5 <em><a title="Isomerase" href="http://en.wikipedia.org/wiki/Isomerase">Isomerases</a></em>: catalyze <a title="Isomer" href="http://en.wikipedia.org/wiki/Isomer">isomerization</a> changes within a single molecule</li> <li>EC 6 <em><a title="Ligase" href="http://en.wikipedia.org/wiki/Ligase">Ligases</a></em>: join two molecules with <a title="Covalent bond" href="http://en.wikipedia.org/wiki/Covalent_bond">covalent bonds</a></li>
</ul>
<p>The complete nomenclature can be browsed at <a relclass="nofollowexternal free" title="http://www.chem.qmul.ac.uk/iubmb/enzyme/" classrel="external freenofollow" href="http://www.chem.qmul.ac.uk/iubmb/enzyme/">http://www.chem.qmul.ac.uk/iubmb/enzyme/</a>.</p>
<p><a id="Industrial_applications" name="Industrial_applications"></a></p>
<h2><span class="editsection">[<a title="Edit section: Industrial applications" href="http://en.wikipedia.org/w/index.php?title=Enzyme&action=edit&section=22">edit</a>]</span> <span class="mw-headline">Industrial applications</span></h2>
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<td align="center" width="24%" align="center"><strong>Application</strong></td> <td align="center" width="38%" align="center"><strong>Enzymes used</strong></td> <td align="center" width="38%" align="center"><strong>Uses</strong></td>
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<td rowspan="2" style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid" rowspan="2"><strong><a title="Baking" href="http://en.wikipedia.org/wiki/Baking">Baking industry</a></strong>
<div class="center">
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<div class="thumbinner" style="widthWIDTH: 182px;" ><a class="thumbinnerinternal"><a title="alpha-amylase catalyzes the release of sugar monomers from starch" class="internal" href="http://en.wikipedia.org/wiki/Image:Amylose.svg"><img widthclass="180thumbimage" height="73" classalt="alpha-amylase catalyzes the release of sugar monomers from starch" width="thumbimage180" longdesc="/wiki/Image:Amylose.svg" alt="alpha-amylase catalyzes the release of sugar monomers from starch" src="http://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Amylose.svg/180px-Amylose.svg.png" /></a>
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<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Amylose.svg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
alpha-amylase catalyzes the release of sugar monomers from starch</div>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Fungus" href="http://en.wikipedia.org/wiki/Fungus">Fungal</a> alpha-amylase enzymes are normally inactivated at about 50 degrees Celsius, but are destroyed during the baking process.</td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Catalyze breakdown of starch in the <a title="Flour" href="http://en.wikipedia.org/wiki/Flour">flour</a> to sugar. Yeast action on sugar produces carbon dioxide. Used in production of white bread, buns, and rolls.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Baby food" href="http://en.wikipedia.org/wiki/Baby_food">Baby foods</a></strong></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Trypsin" href="http://en.wikipedia.org/wiki/Trypsin">Trypsin</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">To predigest baby foods.</td>
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<td rowspan="6" style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid" rowspan="6"><strong><a title="Brewing" href="http://en.wikipedia.org/wiki/Brewing">Brewing industry</a></strong>
<div class="center">
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<div class="thumbinner" style="widthWIDTH: 182px;" ><a class="thumbinnerinternal"><a title="Germinating barley used for malt." class="internal" href="http://en.wikipedia.org/wiki/Image:Sjb_whiskey_malt.jpg"><img widthclass="180thumbimage" height="135" classalt="Germinating barley used for malt." width="thumbimage180" longdesc="/wiki/Image:Sjb_whiskey_malt.jpg" alt="Germinating barley used for malt." src="http://upload.wikimedia.org/wikipedia/commons/thumb/3/32/Sjb_whiskey_malt.jpg/180px-Sjb_whiskey_malt.jpg" /></a>
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<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Sjb_whiskey_malt.jpg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Germinating barley used for malt.</div>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Enzymes from barley are released during the mashing stage of beer production.</td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">They degrade starch and proteins to produce simple sugar, amino acids and peptides that are used by yeast for fermentation.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Juice" href="http://en.wikipedia.org/wiki/Juice">Fruit juices</a></strong></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Cellulases, pectinases</td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Clarify fruit juices</td>
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<td rowspan="4" style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid" rowspan="4"><strong><a title="Dairy" href="http://en.wikipedia.org/wiki/Dairy">Dairy industry</a></strong>
<div class="center">
<div class="thumb tnone">
<div class="thumbinner" style="widthWIDTH: 182px;" ><a class="thumbinnerinternal"><a title="Roquefort cheese" class="internal" href="http://en.wikipedia.org/wiki/Image:Roquefort_cheese.jpg"><img widthclass="180thumbimage" height="144" classalt="Roquefort cheese" width="thumbimage180" longdesc="/wiki/Image:Roquefort_cheese.jpg" alt="Roquefort cheese" src="http://upload.wikimedia.org/wikipedia/commons/thumb/9/92/Roquefort_cheese.jpg/180px-Roquefort_cheese.jpg" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Roquefort_cheese.jpg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Roquefort cheese</div>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Rennin" href="http://en.wikipedia.org/wiki/Rennin">Rennin</a>, derived from the stomachs of young <a title="Ruminant" href="http://en.wikipedia.org/wiki/Ruminant">ruminant animals</a> (like calves and lambs).</td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Manufacture of cheese, used to <a title="Hydrolyze" href="http://en.wikipedia.org/wiki/Hydrolyze">hydrolyze</a> protein.</td>
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<td rowspan="2" style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid" rowspan="2"><strong><a title="Starch" href="http://en.wikipedia.org/wiki/Starch">Starch industry</a></strong>
<div class="center">
<div class="thumb tnone">
<div style="widthWIDTH: 208px;"> <table cellspacing="0" style="borderBORDER-RIGHT: 0pt; PADDING-RIGHT: 0pt none ; marginBORDER-TOP: 0pt; paddingPADDING-LEFT: 0pt; backgroundBACKGROUND: transparent none repeat scroll 0% 50%; PADDING-BOTTOM: 0pt; MARGIN: 0pt; BORDER-LEFT: 0pt; PADDING-TOP: 0pt; BORDER-BOTTOM: 0pt; -moz-background-clip: -moz-initial; -moz-background-origin: -moz-initial; -moz-background-inline-policy: -moz-initial;" cellspacing="0">
<tbody>
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<td style="borderBORDER-RIGHT: 0pt; PADDING-RIGHT: 0pt; BORDER-TOP: 0pt; PADDING-LEFT: 0pt; PADDING-BOTTOM: 0pt; MARGIN: 0pt none ; marginBORDER-LEFT: 0pt; paddingPADDING-TOP: 0pt;BORDER-BOTTOM: 0pt"><a titleclass="Glucoseimage" classtitle="imageGlucose" href="http://en.wikipedia.org/wiki/Image:Glucose_Haworth.png"><img widthheight="79" alt="100Glucose" heightwidth="79100" longdesc="/wiki/Image:Glucose_Haworth.png" alt="Glucose" src="http://upload.wikimedia.org/wikipedia/commons/thumb/6/64/Glucose_Haworth.png/100px-Glucose_Haworth.png" /></a></td> <td style="borderBORDER-RIGHT: 0pt; PADDING-RIGHT: 0pt; BORDER-TOP: 0pt; PADDING-LEFT: 0pt; PADDING-BOTTOM: 0pt none ; marginMARGIN: 0pt; paddingBORDER-LEFT: 0pt; widthWIDTH: 2px;PADDING-TOP: 0pt; BORDER-BOTTOM: 0pt"> </td> <td style="borderBORDER-RIGHT: 0pt; PADDING-RIGHT: 0pt; BORDER-TOP: 0pt; PADDING-LEFT: 0pt; PADDING-BOTTOM: 0pt; MARGIN: 0pt none ; marginBORDER-LEFT: 0pt; paddingPADDING-TOP: 0pt;BORDER-BOTTOM: 0pt"><a titleclass="Glucoseimage" classtitle="imageGlucose" href="http://en.wikipedia.org/wiki/Image:Alpha-D-Fructose-structure-corrected.png"><img widthheight="64" alt="100Glucose" heightwidth="64100" longdesc="/wiki/Image:Alpha-D-Fructose-structure-corrected.png" alt="Glucose" src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/a8/Alpha-D-Fructose-structure-corrected.png/100px-Alpha-D-Fructose-structure-corrected.png" /></a></td>
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<td style="borderBORDER-RIGHT: 0pt none ; marginPADDING-RIGHT: 0pt; paddingBORDER-TOP: 0pt;PADDING-LEFT: 0pt; PADDING-BOTTOM: 0pt; MARGIN: 0pt; BORDER-LEFT: 0pt; PADDING-TOP: 0pt; BORDER-BOTTOM: 0pt">
<div class="thumbcaption">Glucose</div>
</td>
<td style="borderBORDER-RIGHT: 0pt none ; marginPADDING-RIGHT: 0pt; paddingBORDER-TOP: 0pt;PADDING-LEFT: 0pt; PADDING-BOTTOM: 0pt; MARGIN: 0pt; BORDER-LEFT: 0pt; PADDING-TOP: 0pt; BORDER-BOTTOM: 0pt"> </td> <td style="borderBORDER-RIGHT: 0pt none ; marginPADDING-RIGHT: 0pt; paddingBORDER-TOP: 0pt;PADDING-LEFT: 0pt; PADDING-BOTTOM: 0pt; MARGIN: 0pt; BORDER-LEFT: 0pt; PADDING-TOP: 0pt; BORDER-BOTTOM: 0pt">
<div class="thumbcaption">Fructose</div>
</td>
</p>
</td>
<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Amylases, amyloglucosideases and glucoamylases</td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Converts <a title="Starch" href="http://en.wikipedia.org/wiki/Starch">starch</a> into <a title="Glucose" href="http://en.wikipedia.org/wiki/Glucose">glucose</a> and various <a title="Inverted sugar syrup" href="http://en.wikipedia.org/wiki/Inverted_sugar_syrup">syrups</a>.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Tenderizing" href="http://en.wikipedia.org/wiki/Tenderizing">Meat tenderizers</a></strong></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Papain" href="http://en.wikipedia.org/wiki/Papain">Papain</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">To soften meat for cooking.</td>
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<td rowspan="4" style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid" rowspan="4"><strong><a title="Detergent" href="http://en.wikipedia.org/wiki/Detergent">Biological detergent</a></strong>
<div class="center">
<div class="thumb tnone">
<div class="thumbinner" style="widthWIDTH: 182px;" ><a class="thumbinnerinternal"><a title="Laundry soap" class="internal" href="http://en.wikipedia.org/wiki/Image:Washingpowder.jpg"><img widthclass="180thumbimage" height="135" classalt="Laundry soap" width="thumbimage180" longdesc="/wiki/Image:Washingpowder.jpg" alt="Laundry soap" src="http://upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Washingpowder.jpg/180px-Washingpowder.jpg" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:Washingpowder.jpg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Laundry soap</div>
</div>
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</td>
<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Primarily <a title="Protease" href="http://en.wikipedia.org/wiki/Protease">proteases</a>, produced in an <a title="Extracellular" href="http://en.wikipedia.org/wiki/Extracellular">extracellular</a> form from <a title="Bacteria" href="http://en.wikipedia.org/wiki/Bacteria">bacteria</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Used for presoak conditions and direct liquid applications helping with removal of protein stains from clothes.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Contact lens" href="http://en.wikipedia.org/wiki/Contact_lens">Contact lens cleaners</a></strong></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Proteases" href="http://en.wikipedia.org/wiki/Proteases">Proteases</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">To remove <a title="Proteins" href="http://en.wikipedia.org/wiki/Proteins">proteins</a> on <a title="Contact lens" href="http://en.wikipedia.org/wiki/Contact_lens">contact lens</a> to prevent infections.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Rubber" href="http://en.wikipedia.org/wiki/Rubber">Rubber industry</a></strong></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Catalase" href="http://en.wikipedia.org/wiki/Catalase">Catalase</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">To generate <a title="Oxygen" href="http://en.wikipedia.org/wiki/Oxygen">oxygen</a> from <a title="Peroxide" href="http://en.wikipedia.org/wiki/Peroxide">peroxide</a> to convert <a title="Latex" href="http://en.wikipedia.org/wiki/Latex">latex</a> into foam rubber.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Paper" href="http://en.wikipedia.org/wiki/Paper">Paper industry</a></strong>
<div class="center">
<div class="thumb tnone">
<div class="thumbinner" style="widthWIDTH: 162px;" ><a class="thumbinnerinternal"><a title="A paper mill in South Carolina." class="internal" href="http://en.wikipedia.org/wiki/Image:InternationalPaper6413.jpg"><img widthclass="160thumbimage" height="120" classalt="A paper mill in South Carolina." width="thumbimage160" longdesc="/wiki/Image:InternationalPaper6413.jpg" alt="A paper mill in South Carolina." src="http://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/InternationalPaper6413.jpg/160px-InternationalPaper6413.jpg" /></a>
<div class="thumbcaption">
<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:InternationalPaper6413.jpg"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
A paper mill in <a title="South Carolina" href="http://en.wikipedia.org/wiki/South_Carolina">South Carolina</a>.</div>
</div>
</div>
</td>
<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Amylase" href="http://en.wikipedia.org/wiki/Amylase">Amylases</a>, <a title="Xylanase" href="http://en.wikipedia.org/wiki/Xylanase">Xylanases</a>, <a title="Cellulase" href="http://en.wikipedia.org/wiki/Cellulase">Cellulases</a> and <a title="Lignin" href="http://en.wikipedia.org/wiki/Lignin">ligninases</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Degrade starch to lower <a title="Viscosity" href="http://en.wikipedia.org/wiki/Viscosity">viscosity</a>, aiding <a title="Sizing" href="http://en.wikipedia.org/wiki/Sizing">sizing</a> and coating paper. Xylanases reduce bleach required for decolorising; cellulases smooth fibers, enhance water drainage, and promote ink removal; lipases reduce pitch and lignin-degrading enzymes remove <a title="Lignin" href="http://en.wikipedia.org/wiki/Lignin">lignin</a> to soften paper.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Photography" href="http://en.wikipedia.org/wiki/Photography">Photographic industry</a></strong></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Protease (ficin)</td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Dissolve <a title="Gelatin" href="http://en.wikipedia.org/wiki/Gelatin">gelatin</a> off scrap <a title="Photographic film" href="http://en.wikipedia.org/wiki/Photographic_film">film</a>, allowing recovery of its <a title="Silver" href="http://en.wikipedia.org/wiki/Silver">silver</a> content.</td>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><strong><a title="Molecular biology" href="http://en.wikipedia.org/wiki/Molecular_biology">Molecular biology</a></strong>
<div class="center">
<div class="thumb tnone">
<div class="thumbinner" style="widthWIDTH: 182px;" ><a class="thumbinnerinternal"><a title="Part of the DNA double helix." class="internal" href="http://en.wikipedia.org/wiki/Image:DNA123_rotated.png"><img widthclass="180thumbimage" height="100" classalt="Part of the DNA double helix." width="thumbimage180" longdesc="/wiki/Image:DNA123_rotated.png" alt="Part of the DNA double helix." src="http://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/DNA123_rotated.png/180px-DNA123_rotated.png" /></a>
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<div class="magnify" style="floatFLOAT: right;" ><a class="magnifyinternal"><a title="Enlarge" class="internal" href="http://en.wikipedia.org/wiki/Image:DNA123_rotated.png"><img widthheight="1511" heightalt="11" altwidth="15" src="http://en.wikipedia.org/skins-1.5/common/images/magnify-clip.png" /></a></div>
Part of the DNA <a title="Double helix" href="http://en.wikipedia.org/wiki/Double_helix">double helix</a>.</div>
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<td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid"><a title="Restriction enzyme" href="http://en.wikipedia.org/wiki/Restriction_enzyme">Restriction enzymes</a>, <a title="DNA ligase" href="http://en.wikipedia.org/wiki/DNA_ligase">DNA ligase</a> and <a title="Polymerases" href="http://en.wikipedia.org/wiki/Polymerases">polymerases</a></td> <td style="borderBORDER-topTOP: 3px solid rgb(170, 170, 170);3px solid">Used to manipulate DNA in <a title="Genetic engineering" href="http://en.wikipedia.org/wiki/Genetic_engineering">genetic engineering</a>, important in <a title="Pharmacology" href="http://en.wikipedia.org/wiki/Pharmacology">pharmacology</a>, <a title="Agriculture" href="http://en.wikipedia.org/wiki/Agriculture">agriculture</a> and <a title="Medicine" href="http://en.wikipedia.org/wiki/Medicine">medicine</a>. Essential for <a title="Restriction enzyme" href="http://en.wikipedia.org/wiki/Restriction_enzyme">restriction digestion</a> and the <a title="Polymerase chain reaction" href="http://en.wikipedia.org/wiki/Polymerase_chain_reaction">polymerase chain reaction</a>. Molecular biology is also important in <a title="Forensic science" href="http://en.wikipedia.org/wiki/Forensic_science">forensic science</a>.</td>
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