Homotropic allostery

The symmetry model (fig. 2.4) of allostery can describe the cooperative binding of substrate to enzyme (homotropic effect), as well as the influence of effector molecules on the activity of enzymes (heterotropic effect). 

The capacities for cooperativity and allosteric regulation elevate enzymes from the level of simple catalysts to that of the regulators of metabolism. In fact, cooperativity and allosteric regulation share a common mechanism—the alteration of the properties of the catalytic site by binding of a ligand to a second site on the enzyme. Cooperativity may be thought of as the homotropic interaction of identical catalytic sites, and allostery as the heterotropic interaction of a catalytic site and a dissimilar site which binds an allosteric modifier. 

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