Cytochrome C (Cyt C) is a well characterized mobile electron transport protein essential to energy conversion in all aerobic organisms. In mammalian cells, this highly conserved protein is normally localized to the mitochondrial intermembrane space. More recent studies have identified cytosolic Cyt C as a factor necessary for activation of apoptosis. Cyt C is translocated from the mitochondrial membrane to the cytosol where it is required for the activation of caspase-3 (CPP32). Cyt C associates with cytochrome C1 and Rieske protein to form comple, Xenopus/Amphibian, III (cytochrome b-c1 comple, Xenopus/Amphibian,) which is involved in cellular respiration.