<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>In <taxon tax_id="4932">Saccharomyces cerevisiae</taxon> (Baker's yeast), monothiol glutaredoxin 5 (Grx5p) is essential for the mitochondrial machinery involved in the synthesis and assembly of iron/sulphur centres [<cite idref="PUB00016830"/>]. Absence of Grx5p leads to constitutive oxidative damage, exacerbating that caused by external oxidants.</p> <p>Proteins in this group contain a conserved structural domain, PICOT-HD (amino acids 46-132 in Grx5p) [<cite idref="PUB00016736"/>].</p> Monothiol glutaredoxin