Cytochrome C1 (also known as Complex III subunit 4) is a protein encoded by the CYC1 gene. Cytochrome is a heme-containing subunit of the cytochrome b-c1 complex, which accepts electrons from Rieske protein and transfers electrons to cytochrome c in the mitochondrial respiratory chain. It is formed in the cytosol and targeted to the mitochondrial intermembrane space. Cytochrome c1 belongs to the cytochrome c family of proteins.