allosteric

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(ăl'ō-stĕr'ĭz'əm) or al·los·ter·y (ə-lŏs'tə-rē)
n.

A change in the activity and conformation of an enzyme resulting from the binding of a compound at a site on the enzyme other than the active binding site.

al'lo·ster'ic (ăl'ō-stĕr'ĭk) adj.

describing protein molecules that are assumed to possess two or more stereospecifically different, non-overlapping receptor sites. One of these, the active site, binds the substrate; the other, the allosteric site, is complementary to the structure of another, or the same, metabolite, the allosteric effector, which binds specifically and reversibly. The formation of the enzyme-allosteric effector complex does not activate or deactivate a reaction involving the effector itself; it is assumed only to bring about a discrete reversible alteration of the molecular structure of the protein, called allosteric transition. This modifies the properties of the active site, changing one or several of the kinetic parameters that characterize the biological activity of the protein. See also Monod-Wyman-Changeux model.

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Pertaining to an effect on the biological function of a protein, produced by a compound not directly involved in that function (an allosteric effector) or to regulation of an enzyme involving cooperativity between multiple binding sites (allosteric sites).

• a. enzymes — any enzymes containing an allosteric site, where effector molecules can bind to increase or decrease the rate of reaction, in addition to an active site for substrate binding. Allosteric enzymes exhibit sigmoidal rather than Michaelis–Menten kinetics.
• a. site — that site on an enzyme molecule which binds with a nonsubstrate molecule, inducing a conformational change that results in an alteration of the affinity of the enzyme for its substrate.