<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>Unlike other glutaredoxins, glutaredoxin 2 (Grx2) cannot reduce ribonucleotide reductase. Grx2 has significantly higher catalytic activity in the reduction of mixed disulphides with glutathione (GSH) compared with other glutaredoxins. The active site residues (Cys9-Pro10-Tyr11-Cys12, in <taxon tax_id="562">Escherichia coli</taxon> Grx2, <db_xref db="SWISSPROT" dbkey="P39811"/>), which are found at the interface between the N- and C-terminal domains are identical to other glutaredoxins, but there is no other similarity between glutaredoxin 2 and other glutaredoxins. Grx2 is structurally similar to glutathione-S-transferases (GST), but there is no obvious sequence similarity. The inter-domain contacts are mainly hydrophobic, suggesting that the two domains are unlikely to be stable on their own. Both domains are needed for correct folding and activity of Grx2. It is thought that the primary function of Grx2 is to catalyse reversible glutathionylation of proteins with GSH in cellular redox regulation including the response to oxidative stress. The N-terminal domain is <db_xref db="INTERPRO" dbkey="IPR004045"/>.</p> Glutaredoxin 2, C-terminal