Involved in cytochrome c oxidase assembly or stability. Imported into the mitochondria via the mitochondrial MIA40-ERV1 machinery. The twin Cx9C motifs are involved in the recognition by the mitochondrial MIA40-ERV1 disulfide relay system and the subsequent transfer of disulfide bonds by dithiol/disulfide exchange reactions to the newly imported protein. Present with 907 molecules/cell in log phase SD medium. Belongs to the COA4 family. Extended N-terminus. Extended N-terminus.