title: Evidence that the platelet plasma membrane does not contain a (Ca2+ + Mg2+)-dependent ATPase.
abstract: The present study was designed to determine the subcellular distribution of the platelet (Ca2+ + Mg2+)-ATPase. Human platelets were surface labeled by the periodate-boro[3H]hydride method. Plasma membrane vesicles were then isolated to a purity of approx. 90% by a procedure utilizing wheat germ agglutinin affinity chromatography. These membranes were found to be 2.6-fold enriched in surface glycoproteins compared to an unfractionated vesicle fraction and almost 7-fold enriched compared to intact platelets. In contrast, the isolated plasma membranes showed a decreased specific activity of the (Ca2+ + Mg2+)-ATPase compared to the unfractionated vesicle fraction. This decrease in specific activity was found to be similar to that of an endoplasmic reticulum marker, glucose-6-phosphatase, and to that of a platelet inner membrane marker, phospholipase A2. We conclude, therefore, that the (Ca2+ + Mg2+)-ATPase is not located in the platelet plasma membrane but is restricted to membranes of intracellular origin.
mesh_terms: D001792:Blood Platelets / Q000201:enzymology*; D001894:Borohydrides; D017301:Ca(2+) Mg(2+)-ATPase / Q000097:blood*; D000252:Calcium-Transporting ATPases / Q000097:blood*; D002462:Cell Membrane / Q000201:enzymology; D002846:Chromatography, Affinity; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007700:Kinetics; D037102:Lectins / Q000378:metabolism; D017830:Octoxynol; D010504:Periodic Acid; D011092:Polyethylene Glycols; D014018:Tissue Distribution; D014909:Wheat Germ Agglutinins
chemical_list: D001894:Borohydrides; D037102:Lectins; D014909:Wheat Germ Agglutinins; D010504:Periodic Acid; D011092:Polyethylene Glycols; D017830:Octoxynol; C009288:metaperiodate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases