Induced Fit Theory

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Induced fit theory is a variation of the lock-and-key theory of enzymatic function. It is proposed that the substrate causes a conformational change in the enzyme such that the active site achieves the exact configuration required for a reaction to occur. The overall effect would be a tighter binding for the substrate and enzyme. Think of it as a lock and key model. There are specific substrates that combine to a specific enzyme. The theory basically states that both enzyme and active site change shape so only a specific substrate bind to the enzyme and creating the wanted products that the reaction creates. There are a number of influences than can change the efficiency of enzyme, the four most important factors are: inhibitors, allosteric factors, pH, and temperature.

There are two types of inhibitors: competitive inhibitors and noncompetitive inhibitors, and their names give a good indication of what they actually do. Competitive inhibitors have a similar structure to the enzyme's substrate, so they can "compete" with the substrate for the active site of an enzyme. Often the enzyme will bond not to its substrate but to the competitive inhibitor, blocking the substrate from the active site and causing the formation of enzyme-substrate complexes to occur at a slower rate. Noncompetitive inhibitors, on the other hand, do not attach to the active site and block the enzyme-substrate complex from forming. Instead, they react with portions of the active site, which results in the changing of its shape. Once the active site's shape is changed, it can no longer attach to the substrate.

Some enzymes have special areas other than the active site. These special areas are sometimes called regulatory sites. Any molecule that attaches to the regulatory site is called an allosteric factor. Allosteric inhibitors join with the regulatory site and change the shape of the entire enzyme (including the active site), thus preventing it from binding with the substrate. However,...
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