COX19 is a mitochondrial assembly factor essential for cytochrome c oxidase (Complex IV) biogenesis in the electron transport chain. COX19 functions as a chaperone protein localized to the mitochondrial intermembrane space and cytoplasm 1, where it acts as a COX11 copper chaperone supporting copper coordination and stimulates SCO2-mediated metalation of COX2 2. In the absence of COX11, COX19 can directly deliver copper to the copper B site of COX1 2. Beyond its canonical mitochondrial role, COX19 regulates cellular copper homeostasis by transducing an SCO1-dependent redox signal to the copper exporter ATP7A 3. COX19 function is particularly critical during iron deficiency stress 4, and operates downstream of LRRK2 as a modulator of copper chaperone redox status in mitochondrial bioenergetics 5. Disease relevance includes potential involvement in Parkinson's disease pathogenesis, where pathogenic LRRK2 mutations disrupt the LRRK2-COX19 signaling axis impairing COX assembly 5. In cancer, COX19 overexpression promotes colorectal cancer progression by enhancing mitochondrial copper content and ATP production 6, 7. Notably, COX19 mutations were not identified in patients with isolated COX deficiency 8, suggesting other assembly factors remain to be characterized in human disease.