Inhibition and Inactivation of Enzymes

Abstract

In addition to their substrates, enzymes also bind substances that reduce their activity. Such binding can be reversible resulting in inhibition, or irreversible resulting in inactivation of the enzyme. We distinguish four types of inhibition:

competitive :

The inhibitor binds only to the free enzyme, not to the enzyme substrate complex. The EI-complex cannot bind substrate and therefore has no catalytic activity.

uncompetitive :

The inhibitor binds only to the enzyme substrate complex, not to the free enzyme. The EIS-complex has no catalytic activity.

noncompetitive :

The inhibitor binds to both the free enzyme and to the enzyme substrate complex. The EI-complex can still bind to the substrate, but the EIS-complex has no catalytic activity.

partial :

The EIS-complex still has some catalytic activity. It can be either partially noncompetitive or partially uncompetitive.

These inhibition types result in characteristic patterns in Lineweaver-Burk-plots.

Inactivators reduce enzymatic activity in a time-dependent manner. Of particular medical use are suicide-inactivators, which have to be converted into the inactivating species by the enzyme itself. These are very specific and often have few side effects.