Identity of calcium-activated neutral proteases from rabbit cardiac and skeletal muscle

The low-calcium-requiring form (mu CANP) and the high-calcium-requiring form (mCANP) of the calcium-activated neutral proteases were purified to near homogeneity from rabbit cardiac muscle. Each of them was compared with the counterpart of skeletal muscle in respect to subunit composition, calcium sensitivity, pH dependency of the activity and peptide map of the fragments produced by S. aureus V8 protease digestion. All results suggested that mCANP and mu CANP from cardiac muscle were almost indistinguishable in various properties with mCANP and mu CANP of skeletal muscle, respectively, showing the lack of tissue-specificity of CANPs among these two tissues. However, the total and the relative contents of mCANP and mu CANP were different among them.