SCO1 (synthesis of cytochrome c oxidase 1) is a mitochondrial copper metallochaperone essential for cytochrome c oxidase (COX) biogenesis. SCO1 functions as a copper-binding protein with conserved cysteines and histidyl residues that coordinate both Cu(I) and Cu(II) ions 1. Together with its paralog SCO2, SCO1 mediates copper delivery to the Cu(A) site of COX subunit II (MT-CO2/COX2) during COX assembly 23. SCO1 and SCO2 have non-overlapping, cooperative functions, with SCO2 acting upstream to facilitate CO II synthesis and serving as a thiol-disulfide oxidoreductase for SCO1's copper-coordinating cysteines 3. In this model, COX17 delivers copper to SCO2, which transfers it to SCO1 for subsequent delivery to the CuA site 2. SCO1 mutations impair copper binding affinity and redox properties, reducing copper transfer efficiency to COX 4. Mutations in SCO1 cause mitochondrial complex IV deficiency with tissue-specific phenotypes 5. Loss of scox function in Drosophila demonstrates that intact COX assembly and activity are required for processes dependent on adequate energy supply 6. SCO1 plays an important role in copper homeostasis regulation through effects on copper transporter CTR1 abundance and localization.