Dehydroascorbic acid reductase

Washburn, M.P., and Wells, W.W. 1999. Identification of the dehydroascorbic acid reductase and thioltransferase (glutaredoxin) activities of bovine erythrocyte glutathione peroxidase. Biochem. Biophys. Res. Commun. 257 567-571. 

DHA can be reduced to RAA by chemical agents, such as hydrogen sulfide or enzymatically, by dehydroascorbic acid reductase. The conversion of DHA to diketogulonic acid (DKG) is irreversible and occurs both aerobically and anaerobically, particularly during heating. This reaction results in loss of biological activity. The total oxidation of RAA may result in the formation of furfural by decarboxylation and dehydration. With subsequent polymerization, the formation of dark-colored pigments results. These compounds affect the color and flavor of certain foods, such as citrus juices, and decrease nutritive value. 

The ascorbic acid is oxidized by ascorbic acid oxidase in the flour dough to dehydroascorbic acid. In turn, the reduction of dehydroascorbic acid is coupled with the oxidation of protein thiol groups by the enzyme dehydroascorbic acid reductase known to be in wheat (133). 

The lipoxygenase and dehydroascorbic acid reductase enzyme systems in dough illustrate how the rheology of proteins can be modified by either the products of enzymic reactions or the coupled oxidation of substrate and thiol groups of the proteins. 

Ascorbic acid in presence of ascorbic acid oxidase and dehydroascorbic acid reductase... 

GST02 Omega Testis 64% identity with GSTOl Dehydroascorbic acid reductase... 

The maintenance of the ascorbic acid in its reduced form thus appears to be dependent on the maintenance of GSH. The results of these experiments support the view that the dehydroascorbic acid reductase which can be demonstrated in vitro in potato extracts is also operative in vivo. During the phase in which ascorbic acid was disappearing there was no evidence for any loss of activity of dehydroascorbic reductase the increase of DHA, as the fall in GSH and the rise in GSSG indicate, appeared to be associated with an impairment of the system responsible for the reduction of GSSG to GSH. 

That this cannot be the only mechanism reducing DHA in plant tissues seems evident from other considerations. Crook and Morgan (1943) found no evidence of the presence of a dehydroascorbic acid reductase in 8 out of 30 species of plants examined. Some plants which have been shown to reduce DHA readily, e.g., hydrangea (Rubin et al., 1937), do not possess an active dehydroascorbic acid reductase. 

Vitamin C is transported into the blood cells in its oxidized form as dehydroascorbic acid, since this form is non-ionized under physiological conditions and is therefore permeable for membranes. It has been postulated that at least human neutrophils are able to oxidize extracellular ascorbic acid for a more efficient uptake into the cells (Washko et al., 1993). This mechanism also represents a part of the biological recycling system for antioxidants. The intracellular dehydroascorbic acid is rapidly reduced again to ascorbic acid by the GSH redox system. This reduction might also be mediated by the still hypothetical dehydroascorbic acid reductase. 

Wells, W. W., Xu, D. P., Yang, Y., and Rocque, P. A., 1990, Mammalian thioltransferase (glutaredox-in) and protein disulfide isomerase have dehydroascorbic acid reductase activity, J. Biol. Chem. 265 15361-15364. 

Two years after Pfankuch s report, Hopkins and Morgan (45) demonstrated that fresh cabbage and cauliflower juice could catalyze the oxidation of GSH by dehydroascorbic acid. The reaction proceeded according to equation (9). The enzyme responsible for catalyzing the reaction is now known as dehydroascorbic-acid reductase. 

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