Apaf 1 (apoptosis protease-activating factor-1) is a key regulator of the mitochondrial apoptotic pathway, being the central element of the multimeric apoptosome. The apoptosome consists of cytochrome c, procaspase-9 and seven Apaf 1 monomers, and is considered to be core apoptotic machinery that executes mitochondria-dependent apoptosis. Cytochrome c, normally compartmentalized in the mitochorndria, is released into the cytoplasm following apoptotic stimuli. Apaf 1 binds cytochrome c in the cytoplasm and in the presence of dATP/ATP forms the apoptosome. The apoptosome binds procaspase-9 and promotes its autocatalytic activation. Active caspase-9, in turn, activates downstream caspases including 3, 6, and 7 contributing to the proteolytic caspase activation cascade which leads to cell death.