Glutathione and Glutaredoxin – Glutaredoxins (GRX) are small redox enzymes of approximately one hundred amino-acid residues which use glutathione as a cofactor. Glutaredoxins are oxidized by substrates and reduced non-enzymatically by glutathione. In contrast to Thioredoxins, which are reduced by Thioredoxin reductase, no oxidoreductase exists that specifically reduces Glutaredoxins. Instead, Glutaredoxins are reduced by the oxidation of glutathione and reduced glutathione is then regenerated by glutathione reductase. Together these components form the glutathione system. Glutaredoxins function as electron carriers in the glutathione-dependent synthesis of deoxyribonucleotides by the enzyme ribonucleotide reductase. Moreover, Glutaredoxins act in antioxidant defense by reducing dehydroascorbate, peroxiredoxins, and Methione Sulfoxide Reductase. Beside their function in antioxidant defense, bacterial and plant GRX were shown to bind iron-sulfur clusters and to deliver the cluster to enzymes on demand.
L-Glutathione (gamma-L-Glutamyl-L-cysteinyl-glycine) is a tripeptide composed of the amino acids L-glutamine, L-cysteine, and glycine. Glutathione is part of the antioxidant defense system of the cell, together with superoxide dismutase, catalase, alpha-D-tocopherol (vitamin E), ascorbic acid (vitamin C), and others. Glutathione is crucial to cell life, and impairment of the glutathione system results in damage to the cell membrane and cell death.