[Allosteric effect of substrate on sarcoplasmic reticulum Ca-ATPase].

High concentration of ATP is found to activate Ca-dependent ATPase from sarcoplasmic reticulum both in membrane fraction and in purified enzyme preparation. The treatment of Ca-ATPase preparation with tripsin results in the elimination of the activating effect of ATP, which is accompanied by the disappearance of 100.000 molecular weight protein and by the appearance of fragments with molecular weight of 45.000 and 55.000. Repeated freezing of the enzyme preparation eliminates activating effect of ATP. ATP action is analysed from the viewpoint of allosteric kinetics, which postulates the existence of two Ca-ATPase conformers, their mutual conversion being induced by ATP binding at allosteric center. Kinetic parameters of the conformers studied are calculated.