KINETICS AND MECHANISM OF ACETATE KINASE FROM BACILLUS-STEAROTHERMOPHILUS

The initial rates of ATP regeneration catalyzed by acetate kinase (ATP : acetate phosphotransferase; EC 2.7.2.1) from Bacillus stearothermoph ilus were measured under a wide range of MgADP(-), acetyl phosphate, M gATP(2-) and acetate concentrations. The experimental results shelved that the enzyme exhibited positive co-operativity for MgATP2(-) and no co-operativity for MgADP(-), acetyl phosphate and acetate. Furthermor e, the initial rates of the forward reaction, in which MgATP(2-) and a cetate were produced from MgADP(-) and acetyl phosphate, were inhibite d by MgATP(2-) and acetate, and those of the reverse reaction were inh ibited by MgADP(-) and acetyl phosphate. The initial rate data were co rrelated well by using the rate equation derived based on the assumpti on that the reaction obeys the general reaction scheme based on the Ra ndom Bi Bi mechanism, and on the previous experimental result that the enzyme behaves like a dimeric enzyme, even though it is a tetrameric enzyme.