Cells tightly regulate their enzymatic reactions, allowing necessary reactions to proceed while inhibiting unnecessary or damaging ones. One means of regulating enzyme action is allosteric regulation. In allosteric regulation, the covalent modification or noncovalent binding of a regulator to an enzyme can cause an enzyme to change shape and expose an active site. Negative regulation can work this way as well, with the active site becoming hidden.
Enzymes speed up chemical reactions, making reactions occur at the right time and place in a cell. Although enzymes are essential for life, they must be tightly regulated so that cells focus their energy and resources on appropriate cellular reactions. Allosteric regulation occurs when a non-substrate molecule binds or modifies a site other than the active site of an enzyme (called the allosteric site), thereby inducing the enzyme to change its shape. The shape change can result in the activation or inactivation of an enzyme.
Textbook Reference: Concept 3.4 Regulation of Metabolism Occurs by Regulation of Enzymes