Mixed inhibition

Mixed inhibition refers to a combination of two different types of reversible enzyme inhibition – competitive inhibition and uncompetitive inhibition. The term 'mixed' is used when the inhibitor can bind to either the free enzyme or the enzyme-substrate complex. In mixed inhibition, the inhibitor binds to a site different from the active site where the substrate binds. Mixed inhibition results in an decrease in the apparent affinity of the enzyme for the substrate (<math>K_m^{app} > K_m</math>) and a decrease in the apparent maximum enzyme reaction rate (<math>V_{max}^{app} > V_{max}</math>).

Mathematically, mixed inhibition occurs when the factors α and α’ (introduced into the Michaelis-Menten equation to account for competitive and uncompetitive inhibition, respectively) are both greater than 1.

In the special case where α = α’, noncompetitive inhibition occurs, in which case <math>V_{max}^{app}</math> is reduced but <math>K_m</math> is unaffected. This is very unusual in practice