The Phosphocreatine-ATP Energy Shuttle and Muscle Action: Misconceptions, Oversights and Insights

The role of phosphocreatine (PC) as an ‘energy buffer’ in muscular contraction needs to be reassessed from several viewpoints. In particular, the view that the hydrolysis of PC is more exergonic than that of ATP is erroneous, as the enthalpy and Gibbs free energy changes (respectively) have generally been compared. (Apparently, the reactions are about equally exergonic.) Even so, the question of how PC levels build up during the rest phase at the expense of ATP remains. Also, in a general sense, the need for PC is intriguing in itself, as its presence can be obviated by maintaining sufficient levels of ATP. Plausible explanations are proposed for these apparent conundrums.