Cytochrome C is an electron transporting protein that resides within the intermembrane space of the mitochondria, where it plays a critical role in the process of oxidative phosphorylation and production of cellular ATP. An increasing amount of interest has been directed toward the role which cytocrome C has been demonstrated to play in apoptotic processes. Following exposure to apoptotic stimuli, cytochrome C is rapidly released from the mitochondria into the cytosol, an event which may be required for the completion of apoptosis in some systems. Cytosolic cytochrome C functions in the activation of caspase 3, an ICE family molecule that is a key effector of apoptosis.