Ascorbate-induced oxidative inactivation of Zn2+-glycerophosphocholine cholinephosphodiesterase.
Zn2+-glycerophosphocholine cholinephosphodiesterase, responsible for the conversion of glycerophosphocholine into glycerol and phosphocholine, was inactivated during incubation with ascorbic acid at 38 degrees C. The inclusion of copper ions or Fe2+ accelerated the ascorbate-induced inactivation, with Cu2+ or Cu+ being much more effective than Fe2+, suggestive of ascorbate-mediated oxidation. Dehydroascorbic acid had no effect on the phosphodiesterase, but H2O2 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 H2O2 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 Cu2+-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 Cu2+ action. Here, it is proposed that Zn2+-glycerophosphocholine cholinephosphodiesterase is one of brain membrane proteins susceptible to oxidative inactivation.
Sok
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College of Pharmacy, Chungnam National University, Taejon, Korea.
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000494:pharmacology*; D001921:Brain / Q000201:enzymology; D002417:Cattle; D003300:Copper / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006639:Histidine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction / Q000187:drug effects; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D010767:Phosphorylcholine / Q000031:analogs & derivatives / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism*
C033523:4-nitrophenylphosphorylcholine; D000975:Antioxidants; D004791:Enzyme Inhibitors; D010767:Phosphorylcholine; D006639:Histidine; D003300:Copper; D010727:Phosphoric Diester Hydrolases; C061931:glycerophosphocholine cholinephosphodiesterase; D015032:Zinc; D001205:Ascorbic Acid