The Preparation, Properties, and Reactions of Succinyl Coenzyme A Synthetase and Its Phosphorylated Form

A succinyl coenzyme A synthetase preparation from Escherichia coli has the following characteristics: apparent chromatographic, sedimentation, and electrophoretic homogeneity; molecular weight of about 141,000; A280 (1 mg per ml) = 0.511; higher specific activity than previous preparations; and identity by several criteria with a phosphorylated protein (E-P) obtained upon exposure to Mg++, inorganic orthophosphate, and succinyl-CoA or to Mg++ and ATP. ATP will phosphorylate up to 1 histidine residue per mole of enzyme, with an apparent -ΔF of 2000 cal, but more than one phosphoryl group per mole is obtained from exposure to Pi and succinyl-CoA. Capacity of different preparations for E-P formation, as compared to catalytic activity, varies in an unexplained manner. Increases in CoA or succinyl-CoA concentration will cause net Pi formation from E-P. CoA is required for an exchange of Pi with E-P, and slightly stimulates exchange between E-P and ATP.