CHANGES PRODUCED IN MUSCLE PROTEINS DURING INCUBATION OF MUSCLE HOMOGENATES

ABSTRACT Under some experimental conditions, considered analogous to those which may exist in postmortem muscle, changes in the extractability of sarcoplasmic proteins and the composition of myofibrillar and sarcoplasmic proteins were examined. During incubation at neutral pH, degradation of myofibrillar proteins hardly occurred in the absence of Ca ++ , but or‐actinin was released and troponin components were degraded in its presence. Myosin was degraded at acidic pH value regardless of the presence or absence of Ca ++ , which no such effect was observed at the neutral pH value. From these results, the degradation pattern of myofibrillar proteins can be classified as of two types: (1), the degradation of regulatory proteins which is Ca ++ ‐dependent; and (2), that at acidic pH which preferentially includes the degradation of myosin heavy chain. Phosphorylase, which occurs in the sarcoplasm, appears to have an affinity for myofibrils which depends on pH and temperature.