[Ca2+-dependent ATPases of the sarcoplasmic reticulum of skeletal and cardiac muscles and their ion-transporting fragments].

The data are presented on fractionation of cardiac and skeletal muscle Ca2+-ATPase fragments obtained by trypsin and cyanobromide hydrolysis. Amino acid composition of Ca2+-ATPases isolated from the heart and skeletal muscles and of enzyme fragments is determined. The ionophoric properties of the intact enzyme and its fragments are studied. The low-molecular weight enzyme fragment decreases velocity and the level of Ca2+-accumulation by the vesicles of sarcoplasmic reticulum. It is suggested that an "ionphoric" fragment of muscle ATPase is able to form transmembrane Ca2+-selective channel in model lipid membranes.