Calculated Equilibria of Phosphocreatine and Adenosine Phosphates during Utilization of High Energy Phosphate by Muscle

Equations have been derived for calculating the concentrations of ATP, ADP, and AMP in equilibrium with phosphocreatine and creatine by use of association constants for the protonated species and Mg2+ complexes of the reactants and the equilibrium constants for the AMP kinase and creatine kinase reactions.The equations have been used to calculate the expected concentrations of free ATP, ADP, and AMP as high energy phosphate is discharged by a representative muscle.Arguments are advanced for the validity of the results as an estimate of in viva conditions when based only on measured concentrations of phosphocreatine, creatine, and total adenosine phosphates.Changes in phosphocreatine concentration cause rapid changes in the calculated concentrations of ADP and AMP that are consistent with postulated regulatory effects of these compounds on the Embden-Meyerhof pathway.The amount of ADP and AMP formed by a given discharge of high energy phosphate depends upon the H+ concentration, and physiological changes in pH are sufhcient to cause significant changes in the rate of glycolysis in this way.The physiological significance of phosphocreatine as an eff ector is less clear.