Assembly factor for cytochrome c oxidase (respiratory chain complex IV, CIV) (PubMed:35750769). Acts as a COX11 chaperone that supports COX11 copper coordination (PubMed:35750769). Also stimulates SCO2-mediated metalation of COX2 (PubMed:35750769). Required for the transduction of an SCO1-dependent redox signal from the mitochondrion to ATP7A to regulate cellular copper homeostasis (PubMed:23345593). In the absence of COX11, capable of stimulating copper delivery to the copper B site of COX1 (PubMed:35750769). {ECO:0000269|PubMed:23345593, ECO:0000269|PubMed:35750769}. This is the function of COX19 (cytochrome c oxidase assembly factor COX19, Ensembl gene identifier ENSG00000240230).