title: Evidence for a specific phosphatidylinositol 4-phosphate phosphatase in human erythrocyte membranes.
abstract: Human erythrocyte membranes exhibit a specific phosphatidylinositol 4-phosphate phosphohydrolase (PtdIns4P phosphatase) activity which hydrolyzes PtdIns4P and lysoPtdIns4P but not phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) or lysoPtdIns(4,5)P2. Phosphatidic acid, lysophosphatidic acid, glycerophosphoinositol 4-phosphate, glycerophosphoinositol 4,5-bisphosphate, inositol mono, bis, and tris phosphates and several other sugar and nucleoside phosphates are not hydrolyzed. The PtdIns4P phosphatase activity is not affected by Ca2+ or Mg2+ ions nor inhibited by EDTA. Maximum in vitro activity requires non-ionic (Triton X-100) detergents. The phosphatase is very stable in isolated membranes at low temperatures but is rapidly inactivated above 35 degrees C. This critical inactivation temperature is lowered to 20-25 degrees C by solubilizing the membranes with non-ionic detergents. Arrhenius plots of the activity show an inflection at these critical temperatures, suggesting a temperature-dependent change in the environment or conformation of the enzyme. Sulfhydryl-reacting reagents are potent inhibitors. Dithioerythritol stimulates only when the membranes are solubilized with non-ionic detergent. The location of cation-independent PtdIns4P phosphatase activity in the membrane and of Mg2+-dependent PtdIns(4,5)P2 phosphatase activity in the cytosol was also observed for monkey, rabbit, rat, and dog erythrocytes. Both activities are located in the cytosol of sheep erythrocytes.
mesh_terms: D000818:Animals; D003902:Detergents / Q000494:pharmacology; D004285:Dogs; D004910:Erythrocyte Membrane / Q000201:enzymology*; D004912:Erythrocytes / Q000201:enzymology; D000882:Haplorhini; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D017830:Octoxynol; D009928:Organ Specificity; D010744:Phosphoric Monoester Hydrolases / Q000097:blood*; D011092:Polyethylene Glycols / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D012756:Sheep; D013379:Substrate Specificity; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013816:Thermodynamics
chemical_list: D003902:Detergents; D013439:Sulfhydryl Reagents; D011092:Polyethylene Glycols; D017830:Octoxynol; D010744:Phosphoric Monoester Hydrolases; C053153:phosphatidylinositol-3,4-bisphosphate 4-phosphatase; D008274:Magnesium