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Results for “Dehydroascorbic Acid”

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PubMed2000

A single calibration graph for the direct determination of ascorbic and dehydroascorbic acids by electrogenerated luminescence based on Ru(bpy)(3)2+ in aqueous solution

Ascorbic (H2A) and dehydroascorbic (DA) acids were for the first time directly determined in a single chromatographic run by means of the tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)(3)2+) based electrogenerated chemiluminescence (ECL) detection. For the first time, it was demonstrated that DA, a nonelectroactive compound, is ECL active and is responsible for the ECL behavior of H2A. This fact, together with the lack of a DA standard, suggested the use of a calibration graph obtained for H2A, for determining both analytes. The proven ECL activity of DA, together with literature data relative to the standard redox potentials of the different species coming from H2A, led to a reconsideration of the proposed ECL reaction mechanism for H2A. The role of the OH- ion in the reaction mechanism of the two analytes appeared to be crucial. H2A and DA could be separated by a suitable C18-reversed-phase HPLC column using an aqueous 30 mM H3PO4 solution as the mobile phase. The optimal ECL response was achieved by polarizing the working electrode at 1.150 Vvs SCE (standard calomel electrode) (oxidation diffusion limiting potential for both H2A and Ru(bpy)(3)2+). The Ru(bpy)(3)2+ solution, at pH 10 for carbonate buffer, was mixed to the eluent solution in a postcolumn system, obtaining, still at pH 10, the final 0.25 mM Ru(bpy)(3)2+ concentration. The detection limit found for the two analytes was 1 x 10(-7) M. The method was successfully applied to the determination of the analytes in a commercially available orange fruit juice.

Journal Article↗
PubMed1999

Identification of the dehydroascorbic acid reductase and thioltransferase (Glutaredoxin) activities of bovine erythrocyte glutathione peroxidase.

Bovine erythrocyte glutathione (GSH) peroxidase (GPX, EC 1.11.1.9) was examined for GSH-dependent dehydroascorbate (DHA) reductase (EC 1.8.5.1) and thioltransferase (EC 1.8.4.1) activities. Using the direct assay method for GSH-dependent DHA reductase activity, GPX had a kcat (app) of 140 +/- 9 min-1 and specificity constants (kcat/Km(app)) of 5.74 +/- 0.78 x 10(2) M-1s-1 for DHA and 1.18 +/- 0.17 x 10(3) M-1s-1 for GSH based on the monomer Mr of 22,612. Using the coupled assay method for thioltransferase activity, GPX had a kcat (app) of 186 +/- 9 min-1 and specificity constants (app) of 1. 49 +/- 0.14 x 10(3) M-1s-1 for S-sulfocysteine and 1.51 +/- 0.18 x 10(3) M-1s-1 for GSH based on the GPX monomer molecular weight. GPX has a higher specificity constant for S-sulfocysteine than DHA, and both assay systems gave nearly identical specificity constants for GSH. The DHA reductase and thioltransferase activities of GPX adds to the repertoire of functions of this enzyme as an important protector against cellular oxidative stress.

Animals↗