 Cytochrome c binds to Apoptosis Activation Factor 1 (Apaf-1,) which is constitutively expressed in the cytoplasm.
This complex cleaves off caspase-9 precursor's third domain. This allows the molecule to change conformation, and bind to another cleaved caspase-9 precursor, forming a homodimer.
Caspase-9 is autocatalytic: it activates other caspase-9s by cleaving off their third domain. This is known as the "Caspase Cascade." Caspase-9 also activates caspase-3. (Caspase-3 is not autocatalytic.)
Caspase-3 and -9 activate other caspases, cleave enzymes, and activate endonucleases.
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