Required for mitochondrial cytochrome c oxidase (COX) assembly and respiration. Binds copper. May be involved in copper trafficking and distribution to mitochondrial COX and SOD1. Interacts with CMC2. 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 259 molecules/cell in log phase SD medium. Belongs to the CMC family.