title: Effect of calcium concentration on isolated hamster brain Na-K-, Mg-dependent ATPase.
abstract: In these experiments the effect of different concentrations of calcium on the specific activity of isolated Na-K-ATPase was studied. The result of these investigations showed that calcium at 10(6) and 10(7) M stimulated the Na-K-ATPase activity. These studies also show that at higher calcium concentrations (10(5)-10(3)M), the activity of the enzyme is inhibited. The results from calcium binding to isolated membranes, rich in Na-K-ATPase, strongly suggest the existence of a low-affinity binding site which exhibits a large positive cooperativity. Kd = 2.8 x 10(5) +/- 0.4 x 10(5) M and Hill coefficient of 2.9 +/- 0.2. The calcium concentration (1.9 x 10(5) M sufficient to produce significant (24%) inhibition of the Na-K-ATPase is approximately equal to the Kd observed for calcium binding.
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000201:enzymology*; D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000494:pharmacology*; D006224:Cricetinae; D066298:In Vitro Techniques; D007700:Kinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium