Isolation and characterization of homogeneous acetate kinase from Salmonella typhimurium and Escherichia coli.

Acetate kinase from Salmonella typhimurium and Escherichia coli was purified to electrophoretic homogeneity. The amino acid compositions of both proteins were similar, and the apparent molecular weights were the same, about 40,000 for the putative monomers. The native proteins gave higher molecular weights, suggesting that the enzymes may be oligomers, perhaps with two polypeptide subunits. Steady-state kinetic studies were performed with the enzymes isolated from both organisms and the kinetic constants were determined. The Km values were 0.07 and 7 mM for ATP and acetate, respectively. In contrast to earlier studies using less pure preparations, the homogeneous enzymes from both strains were active only with acetate but not with propionate or butyrate. The enzyme activity was cold-labile, and the length of reactivation time in the presence of Mg X ATP and acetate was dependent on protein concentration, suggesting that the monomer may not be catalytically active. The enzyme was phosphorylated with [gamma-32P]ATP and the phosphoprotein was isolated. Phosphoacetate kinase was capable of transferring the phosphate group to either ADP or acetate. The accompanying paper (Fox, D. K., Meadow, N. D., and Roseman, S. (1986) J. Biol. Chem. 261, 13498-13503) shows that the phosphoryl group of phosphoacetate kinase can also be reversibly transferred to Enzyme I of the phosphoenolpyruvate:glycose phosphotransferase system.