title: The plasma membrane calcium pump: regulation by a soluble Ca2+ binding protein.
abstract: The Ca2+ pump of the plasma membrane of human red blood cells is associated with the activity of a (Ca2+ + Mg2+)-ATPase. Both the ATPase and the pump are stimulated above basal activities by calmodulin, an ubiquitous Ca2+-binding protein. Calmodulin isolated from human red blood cells was shown to be equipotent and equieffective with that isolated from beef brain. Half-maximal activation of ATPase (isolated red blood cell membranes, 37 C) and transport (inside-out red blood cell membrane vesicles, 25 C) were obtained with 2.5 and 4.4 nM calmodulin, respectively. Ca2+ dependence of Ca2+ transport was measured in the absence and in the presence of 50 nM calmodulin. At all Ca2+ concentrations above 2 X 10(-7) M Ca2+, the rate of transport was greater in the presence of calmodulin. The results implicate calmodulin in the regulation of the plasma membrane Ca2+ pump, but the mechanism(s) remain to be elucidated.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D004789:Enzyme Activation; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D010764:Phosphorylase Kinase / Q000378:metabolism
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D000255:Adenosine Triphosphate; D010764:Phosphorylase Kinase; D000252:Calcium-Transporting ATPases; D002118:Calcium