Cleavage of the calpain inhibitor, calpastatin, during postmortem ageing of beef skeletal muscle

The objective of this study was to investigate the contribution of caspase and calpain, on the proteolysis of calpastatin in postmortem beef muscle, by examining the influences of calpain inhibitor MDL-28170 and caspase-3 inhibitor DEVD-CHO on calpastatin degradation and the in vitro proteolysis of calpastatin by caspase-3, -6 and μ-calpain. In this study, both calpain- and caspase-3-inhibitors suppressed postmortem degradation of calpastatin. In vitro treatment of calpastatin with μ-calpain resulted in degradation products similar in size to those occurring naturally in aged beef muscle. With addition of caspase-3, only the 100 kDa degradation fragment was present during the early phase of ageing, and subsequently, was likely to have been inactivated by calpain or other factors. Therefore, calpain was the major contributor to the proteolysis of calpastatin in postmortem beef muscle. While caspase-3 was involved in calpastatin degradation during the early postmortem period, calpastatin maybe plays an important role in bridging the gap between caspase and calpain systems.