Glutathione reductase cystine residues

Electron transfer between pyridine nucleotides and disulfide compounds is catalyzed by several fiavoproteins and three of these are well characterized. Lipoamide dehydrogenase functions in the oxidative decarboxylation of a-keto acids catalyzing the reoxidation of reduced lipoate by NAD+ (18, 19). Glutathione reductase catalyzes electron transfer between NADPH and glutathione ZO-22). Thioredoxin reductase catalyzes the reduction of thioredoxin by NADPH (5) thioredoxin is a protein of 12,000 molecular weight containing a single cystine residue which is the electron acceptor S3). 

It is not surprising that enzymes catalyzing such similar chemical reactions should bear striking similarity to one another both structurally and mechanistically. Lipoamide dehydrogenase (34-38), glutathione reductase (39), and thioredoxin reductase (SO, 31) contain, in addition to FAD, a reactive disulfide which is functional in catalysis. These fiavoproteins consist of two identical or near identical polypeptide chains, each with a reactive cystine residue, and two molecules of FAD (31-36). 

Glutathione reductase amino acid composition, 102,104,105 cystine residues, 104 kinetic studies, 138-141 mechanism, 94, 97-98,134 metabolic functions, 129-133 reaction catalyzed, 92 reduction of, 112, 113 specificity of, 92-93 coenzymes and, 94 thiol groups, 141-142 two-electron-reduced enzyme, properties, 133-138... 

Certain oxidation products of proteins, such as oxidation of Cys to cystine, and Met residues to methionine sulfoxide can be repaired by enzymes such as glutathione reductase and methionine sulfoxide (Gabbita et al., 1999 Moskovitz et al.,... 

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