Competitive inhibition

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Competitive inhibition is a form of enzyme inhibition where binding of the inhibitor to the enzyme prevents binding of the substrate and vice versa.

[edit] Mechanism

Competitive inhibition can occur in two different ways:

In classical competitive inhibition, the inhibitor binds to the same active site as the normal enzyme substrate, without undergoing a reaction. The substrate molecule cannot enter the active site while the inhibitor is there, and the inhibitor cannot enter the site when the substrate is there. In this case, the maximum speed of the reaction is unchanged, while the apparent affinity of the substrate to the binding site is decreased (it means: the K_d dissociation constant is apparently increased). The change in K_m (Michaelis-Menten constant) is parallel to the alteration in K_d. Any given competitive inhibitor concentration can be overcome by increasing the substrate concentration in which case the substrate will outcompete the inhibitor in binding to the enzyme.

In non-classical or allosteric inhibition, the inhibitor binds away from the active site, creating a conformational change in the enzyme such that the substrate can no longer bind to it. Consequently, adding more substrate will not increase the reaction rate. Thus, the reaction rate cannot reach its maximum velocity.