Effects of µ-calpain oxidation on Coregonus peled myofibrillar protein degradation in vitro.

The aim of this study was to evaluate the effect of µ-calpain oxidation on Coregonus peled myofibrillar protein degradation. In the present study, a hydroxyl radical oxidation system was selected to investigate oxidative modification on µ-calpain activity and its degradation on C. peled myofibrillar protein. When subjected to oxidation, the carbonyl content of µ-calpain significantly increased with the increasing of oxidation levels, and oxidation modification promoted the µ-calpain activity. Incubation of C. peled myofibrillar protein with oxidized µ-calpain resulted in the enhanced degradation of myosin heavy chains, actin, and troponin T, but the degradation of desmin at higher levels of oxidation was slightly inhibited, based on sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting. This study suggests that oxidation treatment of µ-calpain could accelerate myofibrillar proteolysis through regulating the enzyme activity during postmortem aging. PRACTICAL APPLICATION: Endogenous proteases, especially µ-calpain, are reported to be involved in fish softening during early postmortem storage, which is critical to muscle quality. The cysteine residues of proteins are particularly sensitive to oxidation. The investigation of the effect of oxidation on µ-calpain (a cysteine protease) activity allows for the monitoring of its role in the postmortem proteolysis of fish myofibrils and the associated softening of fish meat, in an attempt to minimize this softening.