title: Disulfide inhibition of copper-catalyzed oxidation of ascorbic acid: spectrophotometric evidence for accumulation of a stable complex.
abstract: Copper-catalyzed oxidation of ascorbic acid was retarded in the presence of the biological disulfide compounds cystine and oxidized glutathione. The evidence suggested that this effect was due to the formation of a stable complex involving the copper ion, the disulfide compound, and ascorbic acid or a derivative formed during the oxidative process. This indicated that less copper was available for the formation of oxygen complexes which are not as stable as the disulfide complexes. Ellman's reagent (Nbs2) was reduced when it was substituted for the biological disulfides or when added, with EDTA, to solutions in which ascorbic acid, copper ion, and the biological disulfides had been allowed to interact. The complex formed with cystine was detected at 360 nm but the glutathione complex was not detected at this wavelength. It is proposed that disruption of cystine or glutathione complexes by EDTA results in formation of 2,3-diketogulonic acid which acts as a reductant of Ellman's reagent.
mesh_terms: D001205:Ascorbic Acid; D002384:Catalysis; D002413:Cations, Divalent; D003300:Copper; D003553:Cystine; D004220:Disulfides; D004228:Dithionitrobenzoic Acid; D005978:Glutathione; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D013057:Spectrum Analysis
chemical_list: D002413:Cations, Divalent; D004220:Disulfides; D003553:Cystine; D003300:Copper; D004228:Dithionitrobenzoic Acid; D005978:Glutathione; D001205:Ascorbic Acid