Activation mechanism of calcium-activated neutral protease. Evidence for the existence of intramolecular and intermolecular autolyses.

The activation mechanism through limited autolysis of a calcium-activated neutral protease (CANP) with a high sensitivity to calcium ions (microCANP) was analyzed. The rate of autolysis was dependent on microCANP concentration. The reaction was inhibited by high concentrations of digestible substrates but not by a nondigestible substrate. Incubation of microCANP inactivated by N-ethylmaleimide with a small amount of activated microCANP caused the degradation of the former in a manner similar to the autolysis of native microCANP. Immobilized microCANP bound to an anti-microCANP immunoglobulin G column autolyzed on addition of calcium ions. These results show that activation of microCANP through limited autolysis involves both intramolecular and intermolecular reactions.