FAD-dependent sulfhydryl oxidase that regenerates the redox-active disulfide bonds in CHCHD4/MIA40, a chaperone essential for disulfide bond formation and protein folding in the mitochondrial intermembrane space. The reduced form of CHCHD4/MIA40 forms a transient intermolecular disulfide bridge with GFER/ERV1, resulting in regeneration of the essential disulfide bonds in CHCHD4/MIA40, while GFER/ERV1 becomes re-oxidized by donating electrons to cytochrome c or molecular oxygen. May act as an autocrine hepatotrophic growth factor promoting liver regeneration. O2 + 2 R'C(R)SH = H2O2 + R'C(R)S-S(R)CR' Homodimer; disulfide-linked. May form heterodimers of isoform 1 and isoform 2 (PubMed:12180965, PubMed:20593814, PubMed:21383138, PubMed:22224850). Interacts with CHCHD4/MIA40 (PubMed:23676665, PubMed:21383138). Ubiquitously expressed. Highest expression in the testis and liver and low expression in the muscle. The disease is caused by variants affecting the gene represented in this entry. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus. Truncated N-terminus.