Enzyme inhibition

(biochemistry) Prevention of an enzymic process as a result of the interaction of some substance with the enzyme so as to decrease the rate of reaction.

The prevention of an enzymic process as a result of the interaction of some substance with an enzyme so as to decrease the rate of the enzymic reaction. The substance causing such an effect is termed an inhibitor. Enzyme inhibitors are important as chemotherapeutic agents, as regulators in normal control of enzymic processes in living organisms, and as useful agents in the study of biochemistry. See also Antibiotic; Chemotherapy; Enzyme.

Inhibitors have been classified as competitive, noncompetitive, and uncompetitive. The effect of a competitive inhibitor is to bind only free enzyme. This can be reversed by sufficiently increased substrate concentrations, so that essentially all of the enzyme is bound into an enzyme-substrate complex. Since both noncompetitive and uncompetitive inhibitors interact with the enzyme-substrate complex, their effects are not nullified by increased concentrations of substrate. An uncompetitive inhibitor exerts less effect (as percent of control) at low than at high substrate concentrations, since less of the enzyme is in the form of the enzyme-substrate complex, with which it interacts. A noncompetitive inhibitor, which reacts with both free enzyme and the enzyme-substrate complex, exerts comparable effects at all substrate concentrations.

A number of compounds reduce the activity of enzymes; sometimes this is a part of normal metabolic regulation and integration (e.g. the responses to hormones), and sometimes it is the action of drugs. Some inhibitors are reversible, others act irreversibly on the enzymes, and therefore have a longer duration of action (the activity of the enzyme remains low until more has been synthesized).