Glutathione reductase metabolic functions

The pyridine nucleotide-disulfide oxidoreductases, lipoamide dehydrogenase (4), glutathione reductase (5), and thioredoxin reductase (6-8) share so many properties in common that they will be compared and contrasted before being considered separately. As their group name implies, they catalyze the transfer of electrons between pyridine nucleotides and disulfides. In spite of their similarities they function in widely divergent metabolic roles. 

Glutathione reductase catalyzes the virtually irreversible reduction of GSSG by NADPH. Its metabolic function is therefore synonymous with that of the product GSH. Glutathione is the most abundant thiol-disulfide pair in the cell by more than an order of magnitude under most conditions the GSH GSSG ratio is about 20 1 (195). Since the ratio of... 

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... 

Determination of the effective functioning of particular enzymes or metabolic pathways potentially may be useful in demonstrating adequacy of provision. Enzymes in plasma that may be helpful in this regard are glutathione peroxidase as an index of selenium status, and red cell enzymes, such as transketolase (thiamine), glutathione reductase (riboflavin) or transaminase (pyridoxine), or glutathione peroxidase (selenium) are all widely used. Methyltetrahydrofolate reductase is involved in metabolism of homocysteine, hence assessment of plasma homocysteine is a useful measure of... 

Polyamine metabolism by parasites differs in several significant ways from the mammalian host these include, but are not limited to, enzyme half-life, turnover, substrate specificity, types and quantities of polyamines produced. The production of the novel bis glutathionyl spermidine adduct by trypanosomatids, its role as an antioxidant and the protein structure of trypanothione reductase is discussed with respect to the more conventional glutathione reductase system. The role of S-adenosylmethionine and decarboxylated S-adenosylmethionine as critical precursors in the biosynthesis of the higher polyamines is explored with respect to differences in the function and control of the pathway by various parasites. Polyamine biosynthesis in parasites is sufficiently different from that of the host to afford multiple opportunities for drug development, these may be aimed directly at circumventing polyamine biosynthesis or at inhibiting precursors necessary for polyamine synthesis. 

As a component of glutathione peroxidase and the iodothyronine 5 -deiodinases, selenium is an essential micronutrient for humans. Its role in the deiodinase enzymes may be one reason that children require more selenium for growth than adults. Selenium is also a component of the enzyme thioredoxin reductase, which catalyses the NADPH-dependent reduction of the redox protein thioredoxin. Other selenium-containing proteins of unknown functions, including selenoprotein P found in the plasma, have also been identified. Excess selenium administered as selenite and selenate has been shown to be metabolized to methylated compounds and excreted. 

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