Caspase-9 is an initiator caspase, encoded by the CASP9 gene. CASP9 orthologs have been identified in all mammals for which complete genome data are available. Unique orthologs are also present in lizards, lissamphibians, and teleosts.
The aspartic acid specific protease caspase-9 has been linked to the mitochondrial death pathway. It is activated during programmed cell death (apoptosis). Induction of stress signaling pathways JNK/SAPK causes release of cytochrome c from mitochondria and activation of apaf-1 (apoptosome), which in turn cleaves the pro-enzyme of caspase-9 into the active form.
Once initiated caspase-9 goes on to cleave procaspase-3 & procaspase-7, which cleave several cellular targets, including poly ADP ribose polymerase.
Caspase-9 precursor procaspase-9 is present as an inactive monomer before it undergoes a conformational change to a dimer and associates with the apf-1 and cytochrome c complex to form an apoptosome.