A new method for the preparation of a calcium activated neutral protease highly sensitive to calcium ions

A Ca²⁺--activated neutral protease has been purified from chicken skeletal muscle to homogeneity by a new method which employs affinity chromatography on casein CH-Sepharose 4B. SDS polyacrylamide gel electrophoresis shows that the purified enzyme consists of a single polypeptide chain with a molecular weight of 76,000. For half-maximum activity this protease requires 50 μM Ca²⁺ ions and its optimum pH is 7.6. The protease is inhibited by leupeptin, antipain, E-64 and endogenous inhibitor. The purified protease is very labile upon storage; after 3 days at 4°C no detectable activity remained.