- Inhibition or activation of an enzyme by a small regulatory molecule that interacts with the enzyme at a site (allosteric site) other than the active site (at which catalytic activity occurs).The interaction changes the shape of the enzyme, thus affecting the active site of the usual complex between the enzyme and its substrate (the substance on which the enzyme acts). As a result, the enzyme's ability to catalyze a reaction (see catalysis) is either inhibited or enhanced. If the regulatory molecule inhibits an enzyme in the pathway of its own synthesis, the control is said to be feedback inhibition. Allosteric control enables the cell to regulate needed substances rapidly.
* * *in enzymology, inhibition or activation of an enzyme by a small regulatory molecule that interacts at a site (allosteric site) other than the active site (at which catalytic activity occurs). The interaction changes the shape of the enzyme so as to affect the formation at the active site of the usual complex between the enzyme and its substrate (the compound upon which it acts to form a product). As a result, the ability of the enzyme to catalyze a reaction is modified. This is the basis of the so-called induced-fit theory, which states that the binding of a substrate or some other molecule to an enzyme causes a change in the shape of the enzyme so as to enhance or inhibit its activity.The regulatory molecule may be a product of a synthetic pathway and inhibit an enzyme in that pathway (see feedback inhibition), thereby preventing the further formation of itself. Other molecules act as activators; i.e., they interact with an enzyme so as to enhance the binding of the substrate to the enzyme, thus enhancing catalytic activity. The enzyme adenyl cyclase, itself activated by the hormone adrenaline (epinephrine (epinephrine and norepinephrine)), which is released when a mammal requires energy, catalyzes a reaction that results in the formation of the compound cyclic adenosine monophosphate (cyclic AMP). Cyclic AMP, in turn, activates enzymes that metabolize carbohydrates for energy production. A combination of allosteric activation and inhibition thus provides a way by which the cell can rapidly regulate needed substances.
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