This gene encodes a member of the family of pyridine nucleotide oxidoreductases. This protein catalyzes the reduction of thioredoxin, but unlike other mammalian thioredoxin reductases (TRs), it contains an additional glutaredoxin domain, and shows highest expression in testes. Like other TRs, it contains a C-terminal, penultimate selenocysteine (Sec) residue at its active site. The selenocysteine is encoded by the UGA codon, which normally signals translation termination. The 3' UTR of Sec-containing genes have a common stem-loop structure, the sec insertion sequence (SECIS), which is necessary for the recognition of UGA as a Sec codon rather than as a stop signal. Alternatively spliced transcript variants encoding different isoforms have been found for this gene. There is also evidence for the use of a non-AUG (CUG) translation initiation site upstream of, and in-frame with the first AUG, leading to additional isoforms. [provided by RefSeq, May 2010]