allosteric enzyme

An enzyme that has two structurally distinct forms, one of which is active and the other inactive. In the active form, the quaternary structure of the enzyme is such that a substrate can interact with the enzyme at the active site. The conformation of the substrate-binding site becomes al­tered in the inactive form and inter­action with the substrate is not possible. Allosteric enzymes tend to catalyse the initial step in a pathway leading to the synthesis of molecules. The end product of this synthesis can act as a feedback inhibitor and the enzyme is converted to the inactive form, thereby control­ling the amount of product synthe­sized.