Evaluation of the phosphoryl-enzyme intermediate concept in the acetate kinase and hexokinase reactions from kinetic studies

Abstract

The kinetic mechanism of action of Escherichia coli acetate kinase (ATP: acetate phosphotransferase, EC 2.7.2.1) was found to be Ping Pong. This conclusion was alluded to from initial rate experiments and from competitive and product inhibition experiments. The findings are consistent with chemical evidence providing the basis for the participation of a phosphoryl-enzyme intermediate in the reaction. A discussion is presented in which it is shown that an analogous covalent intermediate is most probably not involved in the reaction catalyzed by yeast hexokinase (ATP: d-hexose-6-phosphotransferase, EC 2.7.1.1). Finally, a reinvestigation of the use of isotope competition for segregating kinetic mechanisms of multisubstrate enzymic reactions indicates that the approach is invalid.