Occurrence of Phosphate Exchanges in Muscular Contraction

¹ From the Department of Chemistry, University of Arkansas, Fayetteville, Arkansas

No change in the concentrations of ATP and ADP was found to result from 30 seconds of tetanus of the cat gastrocnemius muscle under essentially anaerobic conditions. Tracer data obtained indicate that there is no redistribution of phosphate between the terminal P of ATP and phosphocreatine, such as would be anticipated if resynthesis of ATP took place by transfer of the phosphate group of phosphocreatine. No evidence was found for equilibration of the isotope between the terminal and middle P's of ATP and the terminal P of ADP, such as would be expected if the myokinase reaction played any significant part in the synthesis of ATP. Little or no AMP was found in either resting or tetanized muscles. The specific activities of the terminal P of ATP and of glucose-6-phosphate remained significantly different at the end of the contraction period. If the formation of lactic acid took place by way of the classical Embden-Meyerhof pathway, then a redistribution of the tracer, with resulting equality of specific activities between these two P groups, would be anticipated. From all these results it is concluded that the energy for contraction is furnished by some other means than the dephosphorylation of ATP.