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Enzyme

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<p>Like all catalysts, enzymes work by lowering the activation energy (<em>E</em><sub>a</sub> or Δ<em>G</em><sup>&Dagger;</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 equilibrium 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-1">[2]</sup> Although almost all enzymes are proteins, not all biochemical catalysts are enzymes, since some RNA molecules called ribozymes also catalyze reactions.<sup class="reference" id="_ref-2">[3]</sup> Synthetic molecules called artificial enzymes also display enzyme-like catalysis.<sup class="reference" id="_ref-3">[4]</sup></p>

<p>Enzyme activity can be affected by other molecules. Inhibitors are molecules that decrease enzyme activity; activators are molecules that increase activity. Many drugs and poisons are enzyme inhibitors. Activity is also affected by temperature, chemical environment (e.g. pH), and the concentration of substrate. Some enzymes are used commercially, for example, in the synthesis of antibiotics. 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 fat 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>

Eduard Buchner</div>

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Ribbon-diagram showing carbonic anhydrase II. The grey sphere is the zinc cofactor in the active site. Diagram drawn from PDB 1MOO.</div>

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<h4><span class="mw-headline">Induced fit model</span></h4>

Diagrams to show the induced fit hypothesis of enzyme action.</div>

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<h3><span class="mw-headline">Coenzymes</span></h3>

Space-filling model of the coenzyme NADH</div>

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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>

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Mechanism for a single substrate enzyme catalyzed reaction. The enzyme (E) binds a substrate (S) and produces a product (P).</div>

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<p>The major contribution of Henri 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 complex. The enzyme then catalyzes the chemical step in the reaction and releases the product.</p>

Saturation curve for an enzyme reaction showing the relation between the substrate concentration (S) and rate (<em>v</em>).</div>

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<h2><span class="mw-headline">Inhibition</span></h2>

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>

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Types of inhibition. This classification was introduced by W.W. Cleland.<sup class="reference" id="_ref-55">[57]</sup></div>

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<p>In many organisms inhibitors may act as part of a feedback mechanism. If an enzyme produces too much of one substance in the organism, that substance may act as an inhibitor for the enzyme at the beginning of the pathway that produces it, causing production of the substance to slow down or stop when there is sufficient amount. This is a form of negative feedback. Enzymes which are subject to this form of regulation are often multimeric and have allosteric binding sites for regulatory substances. Their substrate/velocity plots are not hyperbolar, but sigmoidal (S-shaped).</p>

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>

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<h2><span class="mw-headline">Involvement in disease</span></h2>

Phenylalanine hydroxylase. Created from PDB 1KW0</div>

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alpha-amylase catalyzes the release of sugar monomers from starch</div>

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Germinating barley used for malt.</div>

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Roquefort cheese</div>

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A paper mill in South Carolina.</div>

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Cellulose in 3D</div>

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Laundry soap</div>

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Part of the DNA double helix.</div>

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<ul>

<li>Price, N. and Stevens, L., Fundamentals of Enzymology: Cell and Molecular Biology of Catalytic Proteins Oxford University Press, (1999), <a class="internal" href="http://en.wikipedia.org/w/index.php?title=Special:Booksources&isbn=019850229X">ISBN 0-19-850229-X</a> </li>

<li><a class="external text" title="http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd.chapter.86" rel="nofollow" href="http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=gnd.chapter.86~~" rel="nofollow~~">Nutritional and Metabolic Diseases</a> Chapter of the on-line textbook "Introduction to Genes and Disease" from the NCBI. </li>

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<p><strong>Enzyme-naming conventions</strong></p>

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<li><a class="external text" title="http://www.chem.qmul.ac.uk/iubmb/enzyme/" rel="nofollow" href="http://www.chem.qmul.ac.uk/iubmb/enzyme/~~" rel="nofollow~~">Enzyme Nomenclature</a>, Recommendations for enzyme names from the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology. </li>

<li>Koshland D. The Enzymes, v. I, ch. 7, Acad. Press, New York, (1959) </li>

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<p><strong>Industrial applications</strong></p>

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<li><a class="external text" title="http://www.mapsenzymes.com/History_of_Enzymes.asp" rel="nofollow" href="http://www.mapsenzymes.com/History_of_Enzymes.asp~~" rel="nofollow~~">History of industrial enzymes</a>, Article about the history of industrial enzymes, from the late 1900s to the present times. </li>

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<li><a class="external text" title="http://tutor.lscf.ucsb.edu/instdev/sears/biochemistry/tw-enz/tabs-enzymes-frames.htm" rel="nofollow" href="http://tutor.lscf.ucsb.edu/instdev/sears/biochemistry/tw-enz/tabs-enzymes-frames.htm~~" rel="nofollow~~">Structure/Function of Enzymes</a>, Web tutorial on enzyme structure and function. </li> <li><a class="external text" title="http://www.ebi.ac.uk/intenz/spotlight.jsp" rel="nofollow" href="http://www.ebi.ac.uk/intenz/spotlight.jsp~~" rel="nofollow~~">Enzyme spotlight</a> Monthly feature at the European Bioinformatics Institute on a selected enzyme. </li> <li><a class="external text" title="http://www.amfep.org" rel="nofollow" href="http://www.amfep.org/~~" rel="nofollow~~">AMFEP</a>, Association of Manufacturers and Formulators of Enzyme Products </li> <li><a class="external text" title="http://www.brenda.uni-koeln.de" rel="nofollow" href="http://www.brenda.uni-koeln.de/~~" rel="nofollow~~">BRENDA</a> database, a comprehensive compilation of information and literature references about all known enzymes; requires payment by commercial users. </li> <li><a class="external text" title="http://www.ebi.ac.uk/thornton-srv/databases/enzymes/" rel="nofollow" href="http://www.ebi.ac.uk/thornton-srv/databases/enzymes/~~" rel="nofollow~~">Enzyme Structures Database</a> links to the known 3-D structure data of enzymes in the <a title="Protein Data Bank" href="http://en.wikipedia.org/wiki/Protein_Data_Bank">Protein Data Bank</a>. </li> <li><a class="external text" title="http://us.expasy.org/enzyme/" rel="nofollow" href="http://us.expasy.org/enzyme/~~" rel="nofollow~~">ExPASy enzyme</a> database, links to <a title="Swiss-Prot" href="http://en.wikipedia.org/wiki/Swiss-Prot">Swiss-Prot</a> sequence data, entries in other databases and to related literature searches. </li> <li><a class="external text" title="http://www.genome.jp/kegg/" rel="nofollow" href="http://www.genome.jp/kegg/~~" rel="nofollow~~">KEGG: Kyoto Encyclopedia of Genes and Genomes</a> Graphical and hypertext-based information on biochemical pathways and enzymes. </li> <li><a class="external text" title="http://www-mitchell.ch.cam.ac.uk/macie" rel="nofollow" href="http://www-mitchell.ch.cam.ac.uk/macie~~" rel="nofollow~~">MACiE</a> database of enzyme reaction mechanisms. </li>

<li><a title="MetaCyc" href="http://en.wikipedia.org/wiki/MetaCyc">MetaCyc</a> database of enzymes and metabolic pathways </li>

<li><a class="external text" title="http://www.vega.org.uk/video/programme/19" rel="nofollow" href="http://www.vega.org.uk/video/programme/19~~" rel="nofollow~~">'Face-to-Face Interview with Sir John Cornforth who was awarded a Nobel Prize for work on stereochemistry of enzyme-catalyzed reactions</a> Freeview video by the Vega Science Trust </li>

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