title: Oxidative inactivation of brain alkaline phosphatase responsible for hydrolysis of phosphocholine.
abstract: Alkaline phosphatase, one of the enzymes responsible for the conversion of phosphocholine into choline, was purified from bovine brain membrane, where the phosphatase is bound as glycosylphosphatidylinositol-linked protein, and subjected to oxidative inactivation. The phosphatase activity, based on the hydrolysis of p-nitrophenyl phosphate and phosphocholine, decreased slightly after the exposure to H2O2. Inclusion of Cu2+ in the incubation with 1 mM H2O2 led to a rapid decrease of activity in a time- and concentration-dependent manner. In comparison, the H2O2/Cu2+ system was much more effective than the H2O2/Fe2+ system in inactivating brain phosphatase. In a further study, it was observed that the hydroxy radical scavengers mannitol, ethanol, or benzoate failed to prevent against H2O2/Cu2+-induced inactivation of the phosphatase, excluding the involvement of extraneous hydroxy radicals in metal-catalyzed oxidation. In addition, it was found that both substrates, p-nitrophenyl phosphate and phosphocholine, and an inhibitor, phosphate ion, at their saturating concentrations exhibited a remarkable, although incomplete, protection against the inactivating action of H2O2/Cu2+. A similar protection was also expressed by divalent metal ions such as Mg2+ or Mn2+. Separately, it was found that H2O2/Fe2+-induced inactivation was prevented by p-nitrophenyl phosphate or Mg2+ but not phosphate ions. Thus, it is implied that phosphocholine-hydrolyzing alkaline phosphatase in brain membrane might be one of enzymes susceptible to metal-catalyzed oxidation.
authors.affiliation: College of Pharmacy, Chungnam National University, Taejon, Korea.
authors.forename: D E
authors.initials: DE
authors.lastname: Sok
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D002413:Cations, Divalent / Q000378:metabolism; D002417:Cattle; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D016166:Free Radical Scavengers / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D006868:Hydrolysis; D007202:Indicators and Reagents; D007501:Iron / Q000378:metabolism / Q000494:pharmacology; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction; D010767:Phosphorylcholine / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; D016166:Free Radical Scavengers; D007202:Indicators and Reagents; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D016877:Oxidants; D010767:Phosphorylcholine; C008644:nitrophenylphosphate; D003300:Copper; D006861:Hydrogen Peroxide; D007501:Iron; D000469:Alkaline Phosphatase