Cytochrome c controls cellular electron transport and energy metabolism. It is involved in the transfer of electrons between complex III and complex IV in the mitochondrial electron transport chain. It is involved in apoptosis and activates the death protease caspase-3 (CCP32). The presence of Bcl-2 on the organelles inhibits the release of cytochrome c from mitochondria during apoptosis. Along with Apaf-1, and procaspase-9, it forms an essential component of vertebrate ”apoptosome”. Activation of caspase-9 and other capsases directs apoptosis. Serum cytochrome c is a sensitive apoptotic marker in vivo, and increased serum cytochrome c level can serve as a negative prognostic marker.
