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KMID : 0376219810180020321
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Chonnam Medical Journal
1981 Volume.18 No. 2 p.321 ~ p.330
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Nonenzymatic Oxidative Actions of Ascorbate and Dihydroxyfumarate
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Abstract
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Ascorbate and dihydroxyfumarate can, at pH 7.4, nonenzymatically hydroxylate p-nitrophenol, and dioxygenate L-tryptophan to produce 4-nitrocatechol and formylkynurenine, respectively. They also caused the oxidative breakdown of oxyhemoglobin, peroxidation of erythrocyte membrane preparation, and inactivation of erythrocyte membrane-bound enzymes. These actions were stimulated by ferrous iron and EDTA except for the case of hemoglobin oxidation, which was merkedly inhibited by the presence of ferrous iron and EDTA.
However, these oxidative reactions were affected differently by superoxide dismutase, catalase, and peroxidase. That is, the ascorbate-induced oxidations were not affected by superoxide dismutase, indicating that superoxide radical was not involved in the ascorbate-induced reactions. In contrast, catalase and peroxidase markedly inhibited the ascorbate-induced hydroxylation of p-nitrophenol and oxidative breakdown of oxyhemoglobin, whereas ascorbate-induced peroxidation of erythrocyte membrane and inactivation of membrane-bound enzymes were not significantly inhibited by catalase and peroxidase. On the other hand, the p-nitrophenol hydroxylation and hemoglobin oxidation by dihydroxyfumarate were markedly inhibited by catalase or peroxidase, and less effectively by superoxide dismutase. The dihydroxyfumarate-induced membrane peroxidation was inhibited about 30% by catalase, but the inactivation of erythrocyte-bound enzymes by dihydroxyfumarate was not inhibited by these enzymes.
These results suggest that H2O2 but not superoxide radical, plays a primary
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