Failure of Arsenate to Uncouple the Phosphotransacetylase System in Clostridium Acidiurici.

Sagers, Richard D. (Brigham Young University, Provo, Utah), Moshe Benziman, and Sigrid M. Klein. Failure of arsenate to uncouple the phosphotransacetylase system in Clostridium acidiurici. J. Bacteriol. 86:978-984. 1963.-The conversion of pyruvate to acetyl phosphate by extracts of Clostridium acidiurici required coenzyme A (CoA), an electron-carrier system (ferredoxin and nicotinamide adenine dinucleotide), and a divalent metal. Other cofactors may be involved but are not presently defined. The metal activates the system transferring acetyl units between CoA and phosphate. Acetyl CoA could be generated from pyruvate or from acetyl phosphate, but in both cases arsenate failed to uncouple the high-energy acyl compounds. The rate of acetyl transfer between acetyl phosphate and CoA was markedly decreased by 0.005 m arsenate, but the generation of acetyl CoA from pyruvate was essentially unaffected until the arsenate concentration exceeded 0.02 m. Close agreement was observed between the amount of pyruvate utilized and the amount of acetyl phosphate formed, both in the presence and absence of arsenate. The CoA-dependent exchange of P(32)O(4) ( identical with) with acetyl phosphate proceeded at a rate approximately one-eightieth of the rate of acetylation of CoA, indicating an equilibrium value for the phosphotransacetylase reaction similar to that observed for Clostridium kluyveri. The failure of arsenate to uncouple the C. acidiurici enzyme may indicate a high degree of specificity in relation to the acetyl unit acceptor, giving preference to phosphate over arsenate.