COX19 is an assembly factor for cytochrome c oxidase (respiratory chain complex IV, CIV). It acts as a chaperone for COX11 and supports COX11 copper coordination. It also stimulates SCO2-mediated metalation of COX2, and in the absence of COX11 it can stimulate copper delivery to the copper B site of COX1. COX19 is also required for the transduction of an SCO1-dependent redox signal from the mitochondrion to ATP7A, which regulates cellular copper homeostasis.

The COX19 protein belongs to the COX19 family and is assigned to the HGNC gene group of mitochondrial respiratory chain complex assembly factors. UniProt records its localisation in the cytosol, the mitochondrion and the mitochondrial intermembrane space. The mouse ortholog is Cox19. The COX19 gene encodes a cytochrome c oxidase assembly protein, and studies of the S. cerevisiae Cox19 protein suggest a role in metal transport to the mitochondrial intermembrane space and in assembly of complex IV.

The gene was originally named as a human homologue of the yeast gene, hence previous HGNC names such as COX19 cytochrome c oxidase assembly homolog (S. cerevisiae). Researchers studying COX19 are usually interested in how copper is routed to the catalytic core of cytochrome c oxidase and how mitochondrial redox signals feed back on copper handling in the cell.