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 have a function in liver regeneration and spermatogenesis. O2 + 2 R'C(R)SH = H2O2 + R'C(R)S-S(R)CR' Homodimer; disulfide-linked (PubMed:12717032, PubMed:22948913). Interacts with CHCHD4/MIA40 (By similarity).