FIG. 1.

Cartoon of quiescin sulfhydryl oxidase 1 (QSOX1)-L, a 747 amino acid sulfhydryl oxidase. Thioredoxin domains are labeled TRX1 and TRX2. TRX2 does not contain CxxC. ERV/ALR domains (amino acids 396–503) contain 2 CxxC sequences and an FAD-binding domain. FAD binds between the α3 and α4 helices in the QSOX1 protein structure. NEQEQPLGQWHLS peptide is shown (amino acids 631–643) along with the transmembrane domain (amino acids 710–730). QSOX1-S is 604 amino acids and identical in sequence except for amino acids 603 (leucine) and 604 (isoleucine). Molecular oxygen is shown as being reduced by QSOX1 to H₂O₂ as disulfides are formed in the protein. FAD, flavin adenine dinucleotide. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars