Glutaredoxins[1][2][3] (also known as Thioltransferase) are small redox enzymes of approximately one hundred amino-acid residues that use glutathione as a cofactor.

In humans this oxidation repair enzyme is also known to participate in many cellular functions, including redox signaling and regulation of glucose metabolism.

[7] It exists in either a reduced or an oxidized form where the two cysteine residues are linked in an intramolecular disulfide bond.

Glutaredoxins function as electron carriers in the glutathione-dependent synthesis of deoxyribonucleotides by the enzyme ribonucleotide reductase.

Approximately 30 GRX isoforms are described in the model plant Arabidopsis thaliana and 48 in Oryza sativa L. According to their redox-active centre, they are subgrouped in six classes of the CSY[C/S]-, CGFS-, CC-type and 3 groups with additional domains of unknown function.