The ATP-ADP exchange catalyzed by phosphoryl transferase.

Purified phosphoryl transferase catalyzes an ATP-ADP exchange reaction. Evidence is presented which excludes the possibility that the exchange activity of the preparation is due to contaminating adenylate kinase. The rate of the exchange reaction is affected by the molar ratio of ATP to ADP. The reaction is not highly specific either for the divalent metal ion or for the nucleoside triphosphate which serves as phosphoryl donor. Neither inhibitors of oxidative phosphorylation and electron transfer nor uncouplers of oxidative phosphorylation affect the rate of the exchange reaction significantly. Hydroxylamine in high concentration inhibits the exchange reaction. Phosphoryl transferase does not catalyze several other types of reactions which might be expected to involve protein-bound phosphate as intermediates, such as the reactions catalyzed by pyrophosphatase, alkaline phosphatase and succinylthiokinase, respectively. A previously described protein fraction from mitochondria which inhibited the increase in P: 0 ratio induced by the phosphoryl transferase also inhibits the ATP-ADP exchange reaction catalyzed by the transferase. The possible role of phosphoryl transferase in the transfer of a phosphor?/1 group from ATP, formed during oxidative cussed.