inhibition

inhibition
1. (in biochemistry) (enzyme inhibition) A reduction in the rate of an enzyme-catalysed reaction by substances called inhibitors. Competitive inhibition occurs when the inhibitor molecules resemble the substrate molecules and bind to the active site of the enzyme, so preventing normal enzymatic activity. Competitive inhibition can be reversed by increasing the concentration of the substrate. In noncompetitive inhibition the inhibitor binds to a part of the enzyme or enzyme–substrate complex other than the active site, known as an allosteric site. This deforms the active site so that the enzyme cannot catalyse the reaction. Noncompetitive inhibition cannot be reversed by increasing the concentration of the substrate. The toxic effects of many substances are produced in this way. Inhibition by reaction products (feedback inhibition) is important in the control of enzyme activity. See also allosteric enzyme.

2. (in physiology) The prevention or reduction of the activity of neurons or effectors (such as muscles) by means of certain nerve impulses. Inhibitory activity often provides a balance to stimulation of a process; for example, the impulse to stimulate contraction of a voluntary muscle may be accompanied by an inhibitory impulse to prevent contraction of its antagonist.