title: Properties of a membrane-bound phosphatase activity in normal and abnormal red blood cells.
abstract: A neutral, membrane-bound, phosphatase activity was characterized in normal red blood cells, using p-nitrophenylphosphate as substrate. Its specific activity was 1.59 nmol mg-1 min-1. The kinetics were of the Michaelis type: KM,app = 2.5 X 10(-3) M. It was stimulated by K+ and inhibited by ouabain, a behaviour reminiscent of (Na+ + K+)-ATPase. In 10 patients with homozygous sickle cell disease and in 11 patients with unidentified congenital hemolytic anemias, the specific activity was significantly increased. In general, the phosphatase retained Michaelis-Menten kinetics. However, in four patients from the same family with an unidentified hemolytic anemia, the kinetics yielded a biphasic curve instead of a rectangular hyperbola, a change consistent with the existence of an inhibition by substrate excess. From detailed analysis of the curve, the apparent inhibitor constant for pNPP was determined: Ki,app approx. 2.5 X 10(-2) M. This novel abnormality of the red cell membrane might be the distinctive feature of a given type of congenital hemolytic anemia.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000097:blood*; D000745:Anemia, Hemolytic, Congenital / Q000201:enzymology; D000755:Anemia, Sickle Cell / Q000201:enzymology; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology*; D006720:Homozygote; D006801:Humans; D007700:Kinetics; D010042:Ouabain / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000097:blood*; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000097:blood
chemical_list: D010042:Ouabain; D012964:Sodium; D010744:Phosphoric Monoester Hydrolases; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium