In vitro proteolysis of myofibrillar and sarcoplasmic proteins of European sea bass (Dicentrarchus Labrax L) by an endogenous m-calpain

Abstract

The effects of m-calpain isolated from the skeletal muscle of sea bass on sarcoplasmic and myofibrillar proteins isolated from the same tissue were examined in vitro. Incubation of sarcoplasmic proteins with m-calpain resulted in only a slight decrease (0.7 kDa) in the molecular weight (MW) of a 26.5kDa protein. Degradation of myofibrils, monitored by quantification of TCA-soluble peptides generated, resulted in the maximum amount of peptides being generated after 1 h of incubation at 25°C. Noticeable modifications in the SDS-PAGE profile of digested myofibrils were observed, including partial denaturation of myosin heavy chain and the release of tropomyosin, ∼69 and ∼27kDa doublet bands and a few polypeptides of MW lower than 20kDa in the soluble fraction. Examination of the degradation patterns of myofibrillar proteins using Western blotting showed that α-actinin was partially degraded, with release of native α-actinin and its fragments from myofibrils, whereas desmin was highly degraded after 2h of digestion. © 2002 Society of Chemical Industry.