Summary
Evidence has been obtained for the sequential dephosphorylation of Ptdlns(4,5)P2 in human erythrocytes by two specific phosphatases. A Mg\(M{g^{{2^ + }}}\)-dependent phosphatase, partially-purified from cytosol, specifically removes the 5-phosphate from Ptdlns(4,5)P2 and lysoPtdlns(4,5)P2. A cation-independent phosphatase which only hydrolyzes Ptdlns4P and lysoPtdlns4P is localized in the membrane. Maximal hydrolysis of exogenous substrates by both phosphatases requires cationic and nonionic detergents. Under these conditions, \(C{a^{{2^ + }}}\) inhibits the Ptdlns(4,5)P2 phosphatase but not the Ptdlns4P phosphatase by competing with \(M{g^{{2^ + }}}\). Treating the membranes with ATP (or, ADP) and a divalent cation (\(B{a^{{2^ + }}}\), \(M{g^{{2^ + }}}\), \(M{g^{{2^ + }}}\), \(M{g^{{2^ + }}}\)) irreversibly inactivates the Ptdlns4P phosphatase. Endogenous Ptdlns4P and Ptdlns(4,5)P2 are degraded by these enzymes only after membranes are disrupted with Triton X-100. A similar differential location of the two activities was observed in other mammalian erythrocytes. Homogenates of various rat tissues also exhibit cation-independent Ptdlns4P phosphatase activity which, except for brain, exceeds the \(M{g^{{2^ + }}}\)-dependent Ptdlns(4,5)P2 phosphatase activity.
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© 1985 The Humana Press Inc.
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Palmer, F.B.S.C., Mack, S.E. (1985). Hydrolysis of Phosphatidylinositol 4-phosphate and Phosphatidylinositol(4,5)-Bisphosphate by Specific Phosphomonoesterases in Human Erythrocytes. In: Bleasdale, J.E., Eichberg, J., Hauser, G. (eds) Inositol and Phosphoinositides. Experimental Biology and Medicine, vol 6. Humana Press. https://doi.org/10.1007/978-1-4612-5184-2_13
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DOI: https://doi.org/10.1007/978-1-4612-5184-2_13
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