Non-competitive inhibition is a type of inhibition that reduces the maximum rate of a chemical reaction (Vmax) without changing the apparent affinity of the catalyst for binding to the substrate (KmApp in the case of an inhibition enzyme, see kinetics of Michaelis-Menten). A competitive inhibitor is always bound to an allosteric site of the enzyme; however, not all allosteric inhibitors act as competitive inhibitors. Non-competitive inhibition normally applies to enzymes and differs from competitive inhibition in that the inhibitor always binds to the enzyme at a site other than the active site of the enzyme (this site is referred to as the allosteric site). This affects the reaction rate catalyzed by the enzyme since the presence of the inhibitor causes a change in the structure and shape of the enzyme. This change in form implies that the enzyme is no longer able to bind properly to the substrate. This reduces the concentration of "active" enzyme, which causes a decrease in Vmax. In this type of inhibition, there is no competition between the inhibitor and the substrate, so increasing the concentration of the substrate does not produce an increase in the rate of enzyme activity. It is to be noted that although non-competitive inhibition generally implies that the inhibitor does not bind to the active site of the enzyme, the inverse is not true: competitive inhibition may be due to competition by the active site, or by allosteric competitive inhibition .
wiki
