FAD-dependent sulfhydryl oxidase that catalyzes disulfide bond formation. Required for the import and folding of small cysteine-containing proteins in the mitochondrial intermembrane space (IMS). Forms a redox cycle with MIA40 that involves a disulfide relay system. Important for maintaining the cysteine residues in MIA40 in an oxidized state. Reduced ERV1 is reoxidized by cytochrome c. Required for the maturation of cytoplasmic, but not of mitochondrial Fe/S proteins. O2 + 2 R'C(R)SH = H2O2 + R'C(R)S-S(R)CR' Homodimer. Interacts with MIA40, forming transient intermolecular disulfide bridges.