title: Ca2+-activated ATPase of rat liver plasma membrane.
abstract: Rat liver plasma membranes hydrolyze ATP in the presence of Ca2+. The rate of hydrolysis is different when Mg2+ions are present in the incubation system. Several  parameters differentiate Ca2+-ATPase from Mg2+-ATPase: a) the Km of ATP hydrolysis for Ca2+ (2.25 x 10(-4) M) is lower than for Mg2+ (2.14 x 10(-3) M); b) the shape of the activation curve is hyperbolic in the presence of Ca2+ and sigmoid in the presence of Mg2+; c) Mg2+-ATPase shows two different values of activation energy while Ca2+-ATPase presents only a single value; d) Ca2+-ATPase is inhibited, while Mg2+-ATPase is unaffected by cyclic AMP. Ca2+-ATPase is localized on the plasma membrane and is not inhibited by cysteine. It does not hydrolyze substrates different from nucleotides triphosphate, such as glucose-1-phosphate or alpha-glycero-phosphate. The enzyme is probably related to a mechanism of calcium transport.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology*; D000242:Cyclic AMP / Q000494:pharmacology; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008930:Mitochondria, Liver / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D002413:Cations, Divalent; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D010744:Phosphoric Monoester Hydrolases; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium