This domain is found in Quiescin sulfhydryl oxidase (QSOX), an oxidoreductase present in Homo sapiens capable of both generating and transferring disulfide modules within a single polypeptide. The domain is thioredoxin-like, hence referred to as Trx1 domain. Trx1 domain has a di-cysteine motif (Cys-X-X-Cys) which is related to the redox-active domains of protein disulfide isomerase. The Trx1 domain is responsible for intramolecular disulfide transfer through the di-cysteine motif [1].

1: The dynamic disulphide relay of quiescin sulphydryl oxidase. Alon A, Grossman I, Gat Y, Kodali VK, DiMaio F, Mehlman T, Haran G, Baker D, Thorpe C, Fass D; Nature. 2012;488:414-418. PMID:22801504