Free and bound orthophosphate and phosphocreatine in muscle

The use of ethanol at low temperature as deproteinizing medium reveals the presence of some bound phosphocreatine as well as of bound Pi in resting muscle. The amount of bound Pi in muscles of frogs and rabbits is comparable to that bound by myosin isolated from these species, but the amount in cat muscles is significantly greater. The free Pi content is of the order of 3–5 μmoles per gram, and the total of free plus bound Pi is essentially the same whether neutral or acidic deproteinizing agents are used. The data obtained do not give any evidence to support the postulate that muscle contains a P compound more labile to acid than is phosphocreatine.