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  • Title: Oxidative inactivation of brain alkaline phosphatase responsible for hydrolysis of phosphocholine.
    Author: Sok DE.
    Journal: J Neurochem; 1999 Jan; 72(1):355-62. PubMed ID: 9886088.
    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.
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