Monovalent cations requirement of the fructose 1,6-bisphosphate-activated pyruvate kinase from E. coli

The fructose 1,6-bisphosphate-activated pyruvate kinase from Escherichia coli has been purified by a simplified procedure, which gives a homogeneous enzyme in approximately half the working time required by other methods and is suitable for large scale preparations. The activity of the enzyme is strictly dependent on the presence of monovalent cations. Enzyme activity is elicited by K+ and NH4+, but not by Na+. Homotropic cooperativity is displayed in the activation by K+ and NH4+ and heterotropic effects are reciprocally exerted by monovalent cations and other ligands, such as phosphoenolpyruvate and fructose 1,6-bisphosphate. The allosteric nature of such interactions is suggested by changes in heat stability of the enzyme induced by K+ and fructose 1,6-bisphosphate. NH4+, but not K+, at high concentrations, cause an inhibition of enzyme activity.