Characterization of the enolase isozymes of rabbit brain: kinetic differences between mammalian and yeast enolases.

Two isozymes of enolase, alpha alpha and gamma gamma, have been purified from rabbit brain and characterized. The kinetic properties of alpha alpha and gamma gamma (pH optimum, Km for phosphoglycerate and phosphoenolpyruvate, requirement for a divalent cation) are very similar to those of rabbit enolase, form beta beta, and to those of enolase isozymes from other species. However, several novel properties were observed. (i) All the enolases studied were inhibited by Na+ and Li+. (ii) The rabbit enolases, but not yeast enolase, were activated by K+, NH4+, Cs+, and Rb+. (iii) Rabbit enolase is more susceptible to inhibition by excess Mg2+ than is the yeast enolase; the increased inhibition by Mg2+ above pH 7.1 accounts, at least in part, for the observed differences between mammalian and yeast enolases in their pH optima for activity.