<p>Glutaredoxins [<cite idref="PUB00001738"/>, <cite idref="PUB00000560"/>, <cite idref="PUB00002504"/>], also known as thioltransferases (disulphide reductases, are small proteins of approximately one hundred amino-acid residues which utilise glutathione and NADPH as cofactors. Oxidized glutathione is regenerated by glutathione reductase. Together these components compose the glutathione system [<cite idref="PUB00014033"/>]. </p><p>Glutaredoxin functions as an electron carrier in the glutathione-dependent synthesis of deoxyribonucleotides by the enzyme ribonucleotide reductase. Like thioredoxin, which functions in a similar way, glutaredoxin possesses an active centre disulphide bond [<cite idref="PUB00015562"/>]. It exists in either a reduced or an oxidized form where the two cysteine residues are linked in an intramolecular disulphide bond.</p><p>Glutaredoxin has been sequenced in a variety of species. On the basis of extensive sequence similarity, it has been proposed [<cite idref="PUB00005575"/>] that <taxon tax_id="10245">Vaccinia virus</taxon> protein O2L is most probably a glutaredoxin. Finally, it must be noted that <taxon tax_id="10665">Bacteriophage T4</taxon> thioredoxin seems also to be evolutionary related. In position 5 of the pattern T4 thioredoxin has Val instead of Pro.</p><p> This C-terminal domain with homology to glutaredoxin is fused to an N-terminal peroxiredoxin-like domain.</p>