EFFECT OF Ca2+ ON CHANGES IN MYOFIBRILLAR PROTEINS OF BOVINE SKELETAL MUSCLE

Abstract

ABSTRACTThe effects of Ca2+ on the integrity of myofibrils and their proteins were studied by isolating myofibrils from minced at‐death bovine longissimus muscle samples treated with 1 mM Ca2+ and 10 mM oxalate and stored at either 2°C or 23°C. Myofibrils were isolated from treated and control samples at various postmortem times and characterized with SDS‐polyacrylamide gel electrophoresis. In addition, myofibrils were isolated from treated and control samples at various postmortem times and extracted with Hasselbach‐Schneider (H‐S) solution and with 1 mM Tris, pH 8.5. These extracts were characterized with SDS‐polyacrylamide gel electrophoresis. Myofibrils isolated from postmortem muscle samples treated with Ca2+ showed more rapid degradation of troponin T and the concurrent appearance of a 30,000‐dalton component during postmortem storage than did control and oxalate samples. Proteins extracted from myofibrils increased during postmortem storage with both H‐S and Tris solutions. The salt soluble proteins of Ca2+ treated samples showed more 30,000‐dalton component and α‐actinin compared with control and oxalate samples. In essence, the extent and nature of changes in myofibrils and in extracted proteins were dependent upon Ca2+ availability. Storage of muscle samples at room temperature accelerated all these changes. Postmortem modifications in myofibrillar proteins were interpreted as being consonant with the hypothesis that proteolysis of myofibrils is caused by a Ca2+ ‐activated factor endogenous to the muscle fiber.