title: Calmodulin and ATP dependence of the high and low calcium affinity p-nitrophenylphosphatase from human erythrocyte membranes.
abstract: In calmodulin depleted membranes from human erythrocytes, the Ca2+-dependent phosphatase showed different sensitivity to calmodulin and ATP with variable affinity towards free calcium concentrations: a calmodulin-dependent activity with high calcium affinity, K1/2 = 1.2 X 10(-7) mol/l calcium, that was fully activated at submicromolar calcium concentrations, higher concentrations being rather inhibitory; an ATP-dependent activity with lower calcium affinity, K1/2 = 10(-6) mol/l calcium, that was fully activated at 10(-5) mol/l calcium in the presence of 50-200 mumol/l ATP and was insensitive to calmodulin, and a calcium dependent phosphatase that was active at a wider ranger of free calcium, 10(-8)-10(-5) mol/l, and required the presence of both calmodulin and ATP.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000037:antagonists & inhibitors / Q000097:blood*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000097:blood; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000097:blood; D002147:Calmodulin / Q000494:pharmacology; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D004910:Erythrocyte Membrane / Q000201:enzymology*; D006801:Humans; D066298:In Vitro Techniques; D010744:Phosphoric Monoester Hydrolases / Q000097:blood*
chemical_list: D002147:Calmodulin; D000255:Adenosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000252:Calcium-Transporting ATPases; D002118:Calcium; D004121:Dimethyl Sulfoxide