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Title: [Assessment of the role of endogenous regulators in the activation of Ca-ATPase in erythrocyte membranes]. Author: Petruniaka VV, Severina EP, Orlov SN, Bezlepkina TA, Paniushkina EA. Journal: Biokhimiia; 1989 Jun; 54(6):974-9. PubMed ID: 2528995. Abstract: The contribution of calmodulin and protein kinases A or C to the activation of membrane Ca-ATPase was studied on saponin-permeabilized rat erythrocytes. In the presence of all endogenous regulators, the dependence of the Ca-ATPase activity of Ca2+ concentration was described by a bell-shaped curve with a maximum at 2-5 microM Ca2+; K0.5 = 0.43 microM Ca2+. Washing of erythrocyte membranes with 5-10 microM Ca2+ maintained up to 75% of the ATPase activity, while washing with EGTA (2 mM) decreased the activity, on the average, 5-fold, and increased K0.5 up to 0.54-0.6 microM Ca2+. An addition of an EGTA extract to washed membranes restored up to 75% of the original ATPase activity, while calmodulin restored about 40% of the original Ca-ATPase activity and decreased K0.5 to 0.23-0.3 microM Ca2+. The calmodulin inhibitor R24571 failed to alter the Ca-ATPase activity in permeabilized erythrocytes but slightly diminished it in reconstituted membranes. The protein kinase C inhibitors H7 and polymyxin increased the Ca-ATPase activity in permeabilized red cells and suppressed it in reconstituted membranes. The data obtained suggest that in native red cell membranes Ca-ATPase is activated by regulator(s) dependent on Ca2+ and protein kinase which are other than calmodulin.[Abstract] [Full Text] [Related] [New Search]