COENZYME A FUNCTION IN AND ACETYL TRANSFER BY THE PHOSPHOTRANSACETYLASE SYSTEM

Abstract

Lipmann and Tuttle (1) discovered that certain bacterial extracts catalyze a rapid interchange of inorganic and acetyl-bound phosphate. They suggested that this exchange might be due in part to a reversibility of the phosphoroclastic decomposition of pyruvate; however, the observation that the exchange was surprisingly unaffected by addition of acetyl acceptors like formate led them to suspect that unknown factors may be also involved. More recently, Stadtman and Barker (2) reinvestigated the phosphate exchange reaction in cell-free extracts of Clostridium kluyveri. They found that substitution of arsenate for phosphate in these extracts resulted in a very rapid and complete hydrolysis of acetyl phosphate. The marked similarity between these reactions and the reactions catalyzed by the bacterial transglucosidase system, previously described by Doudoroff et al. (3, 4), led to the proposal that the phosphate exchange and arsenolysis reactions of acetyl phosphate were catalyzed by an acetyl-transferring enzyme (Stadtman and Barker (2) ; Lipmann (5)). Concurrently, acetyl phosphate, until recently refractive with regard to acetyl donor function, was found to serve as a G precursor in the synthesis of butyrate and hexanoate by extracts of C. kluyveri (6), and, in particular, it showed a surprising activity in the coenzyme A (CoA)-linked citric acid synthesis by extracts of Escherichia coli (7). These observations became of even greater interest when it was found that microbial extracts could activate acetyl phosphate to serve as an acetyl donor for various CoA-dependent acetylation reactions catalyzed by animal enzyme preparations (8-10). Attempts to identify this “activator” function of microbial extracts led to the proposition that the phosphate exchange and arsenolysis system may be responsible for the acetyl transfer from acetyl phosphate. This possibility prompted us to embark