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Oxidative Inactivation of Brain Alkaline Phosphatase Responsible for Hydrolysis of Phosphocholine
Author(s) -
Sok DaiEun
Publication year - 1999
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1999.0720355.x
Subject(s) - chemistry , phosphatase , alkaline phosphatase , phosphocholine , phosphate , enzyme , biochemistry , oxidative phosphorylation , choline , hydrolysis , catalase , membrane , phospholipid , phosphatidylcholine
: Alkaline phosphatase, one of the enzymes responsible forthe conversion of phosphocholine into choline, was purified from bovine brainmembrane, where the phosphatase is bound as glycosylphosphatidylinositollinkedprotein, and subjected to oxidative inactivation. The phosphatase activity,based on the hydrolysis of p ‐nitrophenyl phosphate andphosphocholine, decreased slightly after the exposure toH 2 O 2 . Inclusion of Cu 2+ in the incubationwith 1 m M H 2 O 2 led to a rapid decrease ofactivity in a time‐ and concentration‐dependent manner. In comparison, theH 2 O 2 /Cu 2+ system was much more effective thanthe H 2 O 2 /Fe 2+ system in inactivating brainphosphatase. In a further study, it was observed that the hydroxy radicalscavengers mannitol, ethanol, or benzoate failed to prevent againstH 2 O 2 /Cu 2+ ‐induced inactivation of thephosphatase, excluding the involvement of extraneous hydroxy radicals inmetalcatalyzed 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 ofH 2 O 2 /Cu 2+ . A similar protection was alsoexpressed by divalent metal ions such as Mg 2+ or Mn 2+ .Separately, it was found thatH 2 O 2 /Fe 2+ ‐induced inactivation was preventedby p ‐nitrophenyl phosphate or Mg 2+ 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.