Cmc1 is a metallo-chaperone like protein which is known to localise to the inner mitochondrial membrane in Saccharomyces cerevisiae. It is essential for full expression of cytochrome c oxidase and respiration []. Cmc1 contains two Cx9C motifs and is able to bind copper(I). Cmc1 is thought to play a role in mitochondrial copper trafficking and transfer to cytochrome c oxidase.