Absence of phosphate interchanges in repetitive muscular contraction

Abstract

In a series of twitches of the gastrocnemius muscle of the cat at the rate of 3/sec. for 1 hour, beginning 5 minutes after the intravenous injection of tracer phosphate, the specific activities of the middle and terminal P groups of ATP, the terminal P group of ADP, and the P group of phosphocreatine were significantly different from each other to approximately the same extent as the specific activities of these P groups in the companion resting muscle. These findings indicate that the function of ATP in the contraction process does not involve any breakdown and resynthesis, and that the creatine kinase and adenylate kinase reactions which serve as means for the synthesis of ATP in isolated enzyme systems, do not play any significant part in muscular contraction.