Cytochrome c is a well conserved electron-transport protein and is part of the respiratory chain localized to mitochondrial intermembrane space. Upon apoptotic stimulation, cytochrome c released from mitochondria associates with procaspase-9/Apaf 1. This complex processes caspase-9 from inactive proenzyme to its active form. This event further triggers caspase-3 activation and eventually leads to apoptosis.
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