Cytochrome C (CYCS) is a small heme protein that belongs to the cytochrome c family. It is found loosely associated with the inner membrane of the mitochondrion. Cytochrome C is a highly soluble protein that functions as a central component of the electron transport chain in mitochondria. CYCS transfers electrons between Complexes III (Coenzyme Q - Cyt C reductase) and IV (Cyt C oxidase). CYCS plays a role in apoptosis. Suppression of the anti-apoptotic members or activation of the pro-apoptotic members of the Bcl-2 family leads to altered mitochondrial membrane permeability resulting in release of cytochrome c into the cytosol. Binding of Cytochrome C to Apaf-1 triggers the activation of caspase-9, which then accelerates apoptosis by activating other caspases.