Extensive Changes during Storage in Carp Myofibrillar Proteins in Relation to Fragmentation.

Abstract

Carp myofibrils were stored in 0.1M NaCl at pH 7.0 in the presence of either 5mM CaCl2 or EGTA at 0°C and 15°C. The degree of fragmentation of the myofibrils in both the Ca and EGTA media increased to 40% within 2 days at 15°C, but the rate at 0°C increased gradually to 38% in Ca medium and 25% in EGTA medium after 7 days. The fragmentation of the myofibrils proceeded simultaneously with increases in the amount of solubilized and released proteins including α-actinin, Mr 43k (or actin), and Mr 34k (or tropomyosin) components from the myofibrils during storage. SDS-PAGE revealed that connectin, nebulin, α-actinin, troponin-T, and troponin-I were extensively degraded and produced peculiar fragments in both media. These protein degrada-tions were detected at an early stage of the storage at 15°C and even at 0°C while the myosin and actin did not change at all. These results suggest that the disintegration of myofibrils caused by solubilization and degradation of myofibrillar proteins is presumed to arise from postmortem tenderization of carp muscle, and may be initiated at the time immediately after death regardless of postmortem increase of Ca2+ that induces rigor mortis.