title: Further characterization of the plasma membrane- and intracellular membrane-associated platelet Ca2+ transport systems.
abstract: Biochemical characterization of the Ca2+-ATPases isolated from human platelet intracellular and plasma membranes is reported. A comparative study of the previously partly described plasma membrane Ca2+-ATPase [Enouf, Bredoux, Bourdeau & Levy-Toledano (1987) J. Biol. Chem. 261, 9293-9297] and the intracellular membrane Ca2+-ATPase obtained simultaneously shows differences in the following parameters: (1) different kinetics of the two enzymes; (2) similar apparent affinity towards Ca2+ (10(-7) M), though the intracellular membrane enzyme was inhibited at Ca2+ concentrations above 10(-6) M; (3) different pH dependence with an activity maximum at pH 7 for the intracellular membrane Ca2+-ATPase and no detectable pH maximum for the plasma membrane Ca2+-ATPase; (4) a 10-fold difference in the ATP requirement of the two Ca2+-ATPases; (5) different patterns of inhibition by vanadate. Finally, the possible regulation of the Ca2+-ATPases was examined by studying the effect of chlorpromazine on the two Ca2+-ATPase activities, with only the plasma membrane enzyme being inhibited. It is concluded that the two platelet Ca2+ transport systems show biochemical differences in spite of the previously shown similarity in the molecular masses of their Ca2+-ATPases, thus conferring a definite specificity to the platelet system.
authors.affiliation: Unité INSERM No. 150, Unité Associée CNRS No. 334, Hôpital Lariboisière, Paris, France.
authors.forename: J
authors.initials: J
authors.lastname: Enouf
authors.forename: R
authors.initials: R
authors.lastname: Bredoux
authors.forename: N
authors.initials: N
authors.lastname: Bourdeau
authors.forename: B
authors.initials: B
authors.lastname: Sarkadi
authors.forename: S
authors.initials: S
authors.lastname: Levy-Toledano
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D001693:Biological Transport, Active; D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000097:blood* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000097:blood*; D002462:Cell Membrane / Q000201:enzymology*; D002746:Chlorpromazine / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000201:enzymology*; D007700:Kinetics; D014638:Vanadates / Q000494:pharmacology
chemical_list: D014638:Vanadates; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium; D002746:Chlorpromazine