Thioredoxin (TXN) is a member of the Thioredoxin family. Thioredoxin exists as a disulfide-linked homodimer and contains one Thioredoxin domain. Thioredoxin is up-regulated by ionizing radiation. Thioredoxin participates in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyzes dithiol-disulfide exchange reactions. Thioredoxin also plays a role in the reversible S-nitrosylation of cysteine residues in target proteins, and thereby contributes to the response to intracellular nitric oxide.