A protein fraction displaying Ca2+-activated proteolytic activity has been isolated from porcine cardiac muscle. The crude enzyme was purified approximately 2000 fold by isoelectric precipitation followed by gel permeation chromatography and by ion exchange chromatography. The partially purified enzyme exhibited optimal activity against either cardiac myofibril or casein substrates between pH 7.5 and 8.0, and in the presence of 1 mm Ca2+ and at least 2 mm 2-mercaptoethanol. The enzyme removes Z-discs from skeletal and cardiac myofibrils and also removes the density from intercalated discs of cardiac myofibrils. The enzyme hydrolyzes troponin-T and troponin-I of both cardiac and skeletal muscle myofibrils in vitro. In its proteolytic effect on either cardiac or skeletal myofibrils and in all other properties examined, the Ca2+-activated, cardiac protease is similar to a Ca2+-activated protease (CAF) recently purified from porcine skeletal muscle (Dayton, W. R., Reville, W. J., Goll, D. E. and Stromer, M. H. (1976) Biochemistry 15, 2159-2167). It is possible that the Ca2+-activated, cardiac protease plays a role in degradation of myofibrils in injured myocardial cells.
- Ca-activated protease
- Intercalated disc