title: Regulation of (Ca2+, Mg2+)-ATPase in human erythrocytes dependent on calcium and calmodulin.
abstract: The enzymatic basis for active Ca2+ transport in erythrocytes, and probably in many other cells, is a Mg2+-dependent Ca2+-ATPase located in the plasma membrane. The Ca2+-ATPase can be prepared in two different forms, a calmodulin-deficient (A-state) and a calmodulin-saturated (B-state). The ATPase is regulated by Ca2+-, K+, and ATP, and these effectors interact in a cooperative way, especially in the B-state. Both A-state and B-state can be solubilized by treatment with Triton X-100. The detergent activates the A-state but reduces the cooperative interactions in both states. The membrane-bound A and B state contain 5 and 25 nmoles calmodulin/g membrane protein, respectively, and the amount of Ca2+-ATPase was estimated at 10--20 nmoles/g membrane protein. It is discussed whether both A and B state represent natives states of the pump-enzymes.
mesh_terms: D017301:Ca(2+) Mg(2+)-ATPase; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000097:blood*; D000252:Calcium-Transporting ATPases / Q000097:blood*; D002147:Calmodulin / Q000097:blood*; D003902:Detergents / Q000494:pharmacology; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D007700:Kinetics; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D003902:Detergents; D011092:Polyethylene Glycols; D017830:Octoxynol; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D011188:Potassium; D002118:Calcium