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Ascorbate‐Induced Oxidative Inactivation of Zn 2+ ‐Glycerophosphocholine Cholinephosphodiesterase
Author(s) -
Sok DaiEun
Publication year - 1998
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.1471-4159.1998.70031167.x
Subject(s) - chemistry , ascorbic acid , superoxide , superoxide dismutase , catalase , dehydroascorbic acid , enzyme , biochemistry , oxidative phosphorylation , histidine , stereochemistry , vitamin c , food science
Zn 2+ ‐glycerophosphocholine cholinephosphodiesterase, responsible for the conversion of glycerophosphocholine into glycerol and phosphocholine, was inactivated during incubation with ascorbic acid at 38°C. The inclusion of copper ions or Fe 2+ accelerated the ascorbate‐induced inactivation, with Cu 2+ or Cu + being much more effective than Fe 2+ , suggestive of ascorbate‐mediated oxidation. Dehydroascorbic acid had no effect on the phosphodiesterase, but H 2 O 2 inactivated the enzyme in a concentration‐dependent manner. Also, the enzyme was inactivated partially by a superoxide anion‐generating system but not an HOCl generator. In support of involvement of H 2 O 2 in the ascorbate action, catalase and superoxide dismutase expressed a complete and a partial protection, respectively. However, hydroxy radical scavengers such as mannitol, benzoate, or dimethyl sulfoxide were incapable of preventing the ascorbate action, excluding the participation of extraneous • OH. Although p ‐nitrophenylphosphocholine exhibited a modest protection against the ascorbate action, a remarkable protection was expressed by amino acids, especially by histidine. In addition, imidazole, an electron donor, showed a partial protection. Separately, when Cu 2+ ‐induced inactivation of the phosphodiesterase was compared with the ascorbate‐mediated one, the protection and pH studies indicate that the mechanism for the ascorbate action is different from that for the Cu 2+ action. Here, it is proposed that Zn 2+ ‐glycerophosphocholine cholinephosphodiesterase is one of brain membrane proteins susceptible to oxidative inactivation.