title: Cation-activated phosphatase activities in islet cell plasma membrane preparations.
abstract: Pancreatic islets from rats or ob/ob mice were homogenized and fractionated either by a two-step or one-step sucrose gradient centrifugation. A plasma membrane enriched fraction was obtained at a sucrose density of about 1.10. The distribution of the plasma membrane probe 125I-wheat germ agglutinin was parallel to that of other plasma membrane markers. Hydrolysis of Mg-ATP-gamma-3Pp in rat islet membranes was of high specific activity, but was little affected by K+ and/or Na+. K+-activated, ouabain-sensitive phosphatase activities were, on the other hand, readily demonstrated in both rat and ob/ob mouse islet membranes. The K+-activated hydrolysis of organophosphate indicators were markedly inhibited by ATP. The binding of 45Ca2+ to mouse islet plasma membranes was increased by ATP. Cation transport and the interaction of Ca2+ with the islet cell plasma membrane may be dependent on phosphoryl-transfer reactions with ATP as the physiological substrate.
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002412:Cations; D002462:Cell Membrane / Q000201:enzymology; D002499:Centrifugation, Density Gradient; D066298:In Vitro Techniques; D007515:Islets of Langerhans / Q000201:enzymology*; D051379:Mice; D008820:Mice, Obese; D009943:Organophosphorus Compounds / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D011188:Potassium / Q000502:physiology; D051381:Rats
chemical_list: D002412:Cations; D009943:Organophosphorus Compounds; D000255:Adenosine Triphosphate; D010744:Phosphoric Monoester Hydrolases; D011188:Potassium; D002118:Calcium