Phosphorylation inhibits the activity of μ-calpain at different incubation temperatures and Ca concentrations in vitro.

This study aimed to investigate the effects of phosphorylation on the activity of μ-calpain and its sensitivity to temperature and Ca. For temperature sensitivity analysis, sarcoplasmic protein was treated with alkaline phosphatase (AP) and phosphatase inhibitor (PI) at 4, 25 and 37°C. The results showed that the degradation degree of μ-calpain in the AP group was significantly higher after incubation for 12h. For calcium sensitivity analysis, samples treated with AP and PI were incubated at 0.01, 0.05, 0.1 and 1mM Ca. The results showed that the degradation rate of μ-calpain was maximum in the AP group and minimum in the PI group at 0.01, 0.05 and 0.1mM Ca. The differences between the three groups reduced as concentration increased. These data demonstrate that phosphorylation plays a negative role in regulating μ-calpain activity. This study clarifies the regulatory mechanism of μ-calpain activation in vitro and/or in postmortem muscle.