Identification of a myofibril-bound serine proteinase in the skeletal muscle of silver carp

Myofibril-bound serine proteinase (MBSP) in the skeletal muscle of silver carp was characterized. Myosin heavy chain (MHC) degraded markedly when silver carp myofibril was incubated at 55-60C as shown by SDS-PAGE. Prolonged incubation of myofibrils also caused the degradation of other myofibrillar proteins such as a-actinin, actin and tropomyosin to some degree. The results suggest the existence of an endogenous myofibril associated proteinase. Serine proteinase inhibitors (Pefabloc SC and Lima bean trypsin inhibitor) greatly suppressed the degradation of myosin heavy chain, while inhibitors for cysteine, metallo, and aspartic proteinases did not show any effect, indicating that the endogeneous proteinase is a myofibril-bound serine proteinase.