Changes

<p>Like all catalysts, enzymes work by lowering the activation energy (<em>E</em>_a or &Delta;<em>G</em>^&Dagger;) 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>