This study was aimed to determine the effect of phosphorylation/dephosphorylation regulated by protein kinase A (PKA) and alkaline phosphatase (AP) on μ-calpain activity at different Ca2+concentrations. μ-Calpain was treated with AP or PKA at 0.01, 0.05, 0.1 and 1 mM Ca2+. The pH value decreased in the AP group but remained stable in the control and PKA groups during incubation. Except samples incubated at 0.01 and 0.1 mM Ca2+for more than 20 min, μ-calpain incubated with PKA showed a higher degree of autolysis than control, but lower than the AP group. The content of α-helix st...