Required for the transduction of an SCO1-dependent redox signal from the mitochondrion to ATP7A to regulate cellular copper homeostasis. May be required for the assembly of mitochondrial cytochrome c oxidase. Interacts with CHCHD4/MIA40 forming transient intermolecular disulfide bridges. Partitions between mitochondria and the cytosol in a copper-dependent manner. Enriched in the cytosol when intracellular copper concentrations are elevated. Belongs to the COX19 family.