Reduction of the selenotrisulfide derivative of glutathione to a persulfide analog by gluthathione reductase

Abstract

The compounds formed by the reaction of selenious acid with glutathione were studied with regard to the effects of pH and g1utathione:selenious acid ratio. At ratios of 4:l or less, and a pH below 2 and above 4, the first stable product is the selenotrisulfide derivative of glutathione (GSSeSG) plus an equimolar quantity of GSSG :GSSeSG free of GSSG was prepared by separating the two compounds on a Dowex 50 column equilibrated with 0.01 M NK12 in 0.1 h4 sodium acetate (pH 4.7) followed by adsorption of the GSSeSG fraction to Dowex 50 Naf at pH 3 and elution with ammonium acetate at pH 5.5. In order to determine the type of selenium compound formed under conditions more nearly simulating physiological conditions of pH and reactant concentrations, 75Se-labeled selenite (1 X 10+ M) was treated with 4 X M G S H at pH 7,25 O, followed by 50 mM iodoacetate. The major selenium compound thus formed was the Se-carboxymethyl derivative of glutathione selenopersulfide (GSSeH) ; this persulfide is believed to be formed by reduction of the initial selenotrisulfide product with excess GSH. Glutathione and elemental selenium were T he fate of selenious acid, or selenite, in systems containing thiols is relevant to many problems regarding the nutritional and toxicological aspects of this substance. Compounds of the type RSSeSR (2-selena-l,3-disulfides or seleno-This is the third paper in a series on selenotrisulfides. rapidly liberated from GSSeSG at pH 7 by 0.1 pg or less of highly purified glutathione reductase from yeast. The reduction of GSSeSG was not catalyzed by lipoyl dehydrogenase, nor was glutathione reductase active when DPNH or selenodicysteine (Cy SSeSCy) was substituted for TPNH or selenodiglutathione. The velocity of GSSeSG reduction was similar to that for GSSG reduction. Evidence was obtained that the initial reaction products were GSH and the selenopersulfide (GSSeH) : glutathione reductase + GSSeSG + TPNH + H+ GSH + GSSeH + TPN+The selenopersulfide rapidly decomposed lo GSH and elemental selenium but could be trapped in the presence of 50 mM iodoacetate as the carboxymethylated derivative, which was identified by thin-layer electrophoresis, thin-layer chromatography, and gel filtration. It is believed that this work provides the first evidence for the selenopersulfide class of compounds. These reactions may have important applications to selenium metabolism and the mechanism of action of selenium as an essential nutrient.trisulfides) have been shown in previous studies to be formed by the reaction of selenious acid with a variety of thiols (Ganther, 1968;Ganther and Corcoran, 1969) in accord with the equation first proposed by Painter (1941) 4RSH + H2Se03 + RSSeSR + RSSR + 3H20 (1)The most abundant thiol in biological systems is glulathione. A specific requirement for glutathione in selenite metabolism has been described (Ganther, 1966). The reaction of glutathione with selenious acid was indicated previously to be more complex than for other thiols (Ganther, 1968) and has now been studied in more detail. The...

Similarities between the Abiotic Reduction of Selenite with Glutathione and the Dissimilatory Reaction Mediated by Rhodospirillum rubrum and Escherichia coli

“…Considering that selenodiglutathione is a moderately stable intermediate that can be isolated from the reaction mixture (9,22) and that the oxidized glutathione accumulates in the reaction mixture, we propose that Reaction 6 develops more slowly than Reaction 7 (Fig. 8).…”

“…Glutathione is proposed to function as electron donor in the reduction. The first intermediary product is selenodiglutathione (GS-Se-SG), which is a substrate for the glutathione reductase (GR) (9) and, according to Björnstedt et al (24), also for the bacterial thioredoxin. The oxidized thioredoxin is regenerated by the thioredoxin reductase (TR).…”

“…Selenodiglutathione-GS-Se-SG was detected by monitoring its absorbance at 260 nm (9). Its appearance and disappearance were followed in a spectrophotometer (Uvikon 860, Kontron, Zü rich, Switzerland).…”

Pharmacology and toxicology of diphenyl diselenide in several biological models

“…The mechanism of oxidation of thiol groups in low-and high-molecular weight molecules by selenium varies with the chemical structure of the compounds and can involve the formation of selenoxides, selenotrisulfides and selenylsulfide (10,11). OS compounds such as selenocystine and a variety of diselenides can react with thiols such as cysteine, dithiothreitol (DTT) and reduced glutathione (GSH) to produce selenocysteine and selenols, respectively, and disulfides.…”

Diphenyl Diselenide and Ascorbic Acid Changes Deposition of Selenium and Ascorbic Acid in Liver and Brain of Mice

“…The aim of this study was to investigate the effect of exposure to (PhSe) 2 and Na 2 SeO 3 , two selenium compounds that oxidize sulfhydryl groups (Tsen & Tapel 1958;Ganther 1968Ganther & 1971Barbosa et al 1998;Maciel et al 2000), into cerebral and hepatic (enzyme) ALA-D and whether simultaneous administration of ascorbic acid, a classical antioxidant, could protect ALA-D inhibition and other toxic signs caused by selenium. The effect of these compounds on selenium distribution, on total non-protein-thiol, ascorbic acid content and haemoglobin was also examined.…”