Oxidized glutathione reductase

The spectra of oxidized glutathione reductase and of the 2-electron-reduced enzyme are shown in Fig. 1. This red intermediate, which has been shown to be functional in catalysis 39), will be referred to as EH2 designating a half-reduced active center it has also been referred to as F (S3, 53), but this can be confused with oxidized flavin in other nomenclatures. Its spectral characteristics are virtually identical with those of the analogous species of lipoamide dehydrogenase 34, 37, 64)- It has... 

The FAD-dependent enzyme glutathione reductase plays a role in the antioxidant system. Glutathione reductase restores reduced glutathione (GSH), the most important antioxidant in erythrocytes, from oxidized glutathione (GSSG) [1, 2]. 

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

Glutathione reductase (GR) catalyzes the reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH) using NADPH provided from the hexose monophosphate pathway. GR, a ubiquitous flavoenzyme, maintains a high value of two for the GSH/GSSG ratio in the red blood cells. l,3-Bis(2-chloroethyl)-nitrosourea (BCNU) selectively inhibits cellular GR. GR is composed of two identical subunits, each of molecular mass 50 kDa (S8). The three-dimensional structure and mechanism of catalysis have been established for human GR (K17). 

The importance of having adequate supplies of NADPH for the regeneration of these various enzymes cannot be over emphasized. In normal situations this cofactor can be adequately provided by the reductive pentose phosphate pathway. Monitoring the activity of the pentose phosphate pathway has been proposed as a unique way to study the metabolic response to oxidative stress, since the glutathione peroxidase activity is coupled via glutathione reductase to the enzyme glucose-6-phosphate dehydrogenase (Ben Yoseph et ah, 1994). 

III. Glutathione reductase (EC 1.6.4.2) It is a flavoprotein that catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG) to glutathione (GSH). This enzyme is essential for the GSH redox cycle which maintains adequate levels of reduced cellular GSH. A high GSH/GSSG ratio is essential for protection against oxidative stress. 

Disulfides can be reduced to two thiols (Fig. 5.14). The best example is the reduction of oxidized glutathione (GSSG) back to the reduced form (GSH) (Fig. 5.14), which is mediated by glutathione reductase. In addition, exchange can occur with other thiols mediated by protein disulfide isomerase. In principle, sulfenic acids can probably also be reduced back to thiols, but because of the reactivity of the sulfenic acid, this is not generally observed. 

The inhibition constant for the process in which the enzyme glutathione reductase is inhibited by G6P was determined by measuring the initial rate of the oxidation of NADPH at various concentrations of GSSG. This procedure was repeated four times, each time with a separate concentration of the inhibitor G6P All the solutions were prepeared in 0.1 M Tris buffer pH 8 containing 10 mM MgCl2 and 0.94 mM EDTA. 

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