Ca2+-induced binding of calpain-2 to myofibrils: Preliminary results in pork longissimus thoracis muscle supporting a role on myofibrillar protein degradation.

Abstract The aim of this study was to investigate the role of Ca2+ in the process of calpain-2 becoming associated to myofibrils and the potential of myofibril-bound calpain to degrade myofibrillar proteins. Different Ca2+ concentrations were applied to myofibrils mixed with partially purified calpain-2. Ca2+ induced binding of calpain to myofibrils in a concentration-dependent manner. The half-maximal Ca2+ requirements for binding of calpain-2 to myofibrils and for calpain-2 proteolysis of myofibrils were 0.60 mM and 0.29 mM, respectively. To investigate the proteolytic activity of myofibril-bound calpain, a mixture of myofibrils and calpain-2 was briefly incubated with Ca2+. Unbound calpain was removed by washing with a Ca2+-free buffer. The myofibril-bound calpain maintained proteolytic activity and degraded desmin when re-activated with Ca2+. In conclusion, the results suggest that an increase in Ca2+ will activate and induce binding of calpain to myofibrils. Subsequently, calpain is relatively tightly bound and proteolytically active.