Molecular Properties of Post‐Mortem Muscle. 6. Effect of Temperature on Protein Solubility of Rabbit and Bovine Muscle

Abstract

SUMMARY– Studies were conducted to investigate the effect of temperature on the actin‐myosin interaction of rabbit and bovine muscle during rigor and post‐rigor shortening. Muscle was stored at four different temperatures (2°, 16°, 25° and 37°), corresponding to three types of post‐mortem muscle shortening: cold, minimal and high temperature. These three types of shortening are presumably related to different states of the actin‐myosin interaction in post‐mortem muscle. Post‐mortem tenderization may be the result of either actin‐myosin dissociation or F‐actin depolymerization.To detect the occurrence of either of these possible changes, two salt solutions, differing widely in their myofibrillar protein extracting abilities, were used to compare post‐mortem myofibrillar protein solubility after different times of post‐mortem storage and to provide information about the actin‐myosin complex. Myofibrillar protein solubility of both rabbit and beef muscle in 0.5M KCl, 0.1M phosphate, pH 7.4, increased markedly with increasing post‐mortem storage at temperatures up to 25deg;. Similar solubility changes were obtained with 1.1M Kl, 0.1M K phosphate, pH 7.4, but these changes were much smaller in magnitude. Solubility in both salt solutions, in general, decreased for muscle stored at 37°.Although time and temperature of post‐mortem storage caused appreciable alterations in protein solubility, these alterations could not be directly related to changes in tenderness or sarcomere length or to species differences in the effects of temperature on post‐mortem shortening. Viscosity, analytical ultracentrifugation, and ATPase assays all indicated the absence of “normal” actomyosin in all myofibrillar protein extracts in this study. It was suggested that the 1.1 M KI extracts contained G‐actomyosin, but the available evidence indicated the presence of only myosin in 3‐hr, 0.5 M KCI extracts.