Thioredoxins reduce disulfide bonds in other proteins using the two cysteines of their conserved active site (WCGPC). They are kept in a reduced, active form by thioredoxin reductase, TrxR, which converts TrxS[[2]] to Trx(SH)[[2]] using NADPH. Thioredoxins have diverse in vivo functions including protection against oxidative stress, redox modification of other proteins, and as an electron donor for ribonucleotide reductase in DNA synthesis. Some thioredoxins are specific to particular organs or cellular compartments. (Adapted from FBrf0200723 and PMID:23397885.)