Succinyl Coenzyme A Synthetase from Escherichia coli

The reaction between coenzyme A and adenosine triphosphate catalyzed by partially purified extracts of Escherichia coli has been studied and its relevance to the mechanism of succinyl coenzyme A synthetase determined. The apparent phosphorylation of coenzyme A by adenosine triphosphate, which had led to the proposal that free coenzyme A phosphate was an intermediate of the succinyl coenzyme A synthetase reaction, is shown to be dependent on an impurity in commercially available coenzyme A. The impurity has been isolated, identified as 3',5'-diphosphoadenosine, and its reaction with adenosine triphosphate shown to be mediated by the sequential action of two enzymes present in partially purified E. coli extracts. The first enzyme, a 3'-nucleotidase, converts 3',5'-diphosphoadenosine to adenosine 5'-monophosphate, and the second enzyme, adenylate kinase, catalyzes the reaction between adenosine 5'-monophosphate and adenosine triphosphate with the formation of 2 eq of adenosine diphosphate. Chromatographically purified coenzyme A does not react with adenosine triphosphate in these enzyme systems.