Identification of acetylphosphate as the product of clostridial glycine reductase: evidence for an acyl enzyme intermediate

It has been reported [Tanaka, H., & Stadtman, T. C. (1979) J. Biol. Chem. 254, 447-452] that glycine reductase from Clostridium sticklandii catalyzes the reaction glycine + ADP + P(i) + 2(e)- - acetate + ATP + NH(4)+. Glycine reductase consists of three proteins, designated A, B, and C. Only A has been purified to homogeneity. A dithiol serves as an electron donor. We find that ADP is not essential for the reaction and that in its absence acetyl phosphate is formed. Upon further purification of components B and C, an acetate kinase activity can be separated from both proteins. This observation establishes that acetate kinase activity is not an intrinsic property of glycine reductase, and therefore the reaction catalyzed by glycine reductase is glycine + P(i) + 2(e)- - acetyl phosphate + NH(4)+. Experiments with [(14)C]glycine and unlabeled acetate show that free acetate is not a precursor of acetyl phosphate. When glycine labeled with l8(O) is converted to product, l8(O) is lost. The l 8 (O) content of unreacted glycine remains unchanged after approximately 50% is converted to product. We propose that an acyl enzyme, most probably an acetyl enzyme,is an intermediate in the reaction and that the acetyl enzyme reacts with P(i) to form acetyl phosphate. A mechanism is proposed for the formation of the acetyl enzyme.