Creatine phosphokinase and the enzymic and contractile properties of the isolated myofibril

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Abstract
At pH 74 in the presence of well-dialyzed aqueous extracts of muscle acetone-powder, creatine phosphate and Mg ions, isolated myofibrils shorten and simultaneously creatine phosphate is split. This shortening process and splitting of creatine phosphate was demonstrated to be due to low concentrations of adenosine diphosphate (ADP) or adenosine triphosphate (ATP) which are associated with the acetone-powder extracts and not readily removed by dialysis. The bound ADP of the myofibril does not catalyze creatine phosphate breakdown in the creatine phosphokinase-myofibril system. The effects of Ca and Mg ions on the liberation of creatine by the acetone-powder ex-tract-myofibril system were described. In the presence of the creatine phosphokinase system, low concentrations of ADP will bring about rapid contraction of isolated myofibrils, whereas a similar concentration of ATP added in the absence of creatine phosphokinase induces little or no change. This observation is taken as evidence that removal of phosphate from ATP is essential for contraction of the isolated myofibril.