Question

Compare and contract between Competitive, Uncompetitive, and Noncompetitive Inhibition.

Answer 1

A competitive inhibitor blocks the enzyme's active site i.e. it occupies the same space as the natural substrate. A competitive inhibitor can only bind to the enzyme, E and not to the enzyme-substrate complex, ES. Therefore a competitive inhibitor increases Km by interfering with the binding of the substrate, but it does not affect Vmax because it cannot change the catalysis in ES.

A non-competitive inhibitor binds to the enzyme somewhere other than the active site of the enzyme (known as an allosteric site). The net effect of a non competitive inhibitor binding is a change in the shape of the enzyme and its active site in such a way that the substrate can no longer interact with the enzyme. A noncompetitive inhibitor decreases Vmax but does not affect Km.

An uncompetitive inhibitor like a non-competitive inhibitor binds to the enzyme on a site different from its active site. However, unlike a non-competitive inhibitor, an uncompetitive inhibitor only binds to the enzyme when substrate is bound to the enzyme. An uncompetitive inhibitor binds to enzyme-substrate complex to stop enzyme from reacting with substrate to form product. The binding of an uncompetitive inhibitor results in a decrease in Km, and Vmax.

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