Caspase-9

Caspases are key effectors of programmed cell death. They are synthesized as inactive proenzymes which are activated by cleavage at a specific aspartate residue to form two subunits. These subunits are normally linked together by a linker which may be involved in the regulation of the different caspases. Caspase-9 is a member of the CED-3 family and bear high similarity to caspase-3. Procaspase-9 can be activated by either caspase-3 or granzyme B, although they cleave the proenzyme to different size subunits. Cleavage by granzyme B produces an active enzyme which is capable of cleaving PARP. Also, the ability of caspase-3 to activate caspase-9 seems to suggest that caspase-9 is further downstream of caspase-3 and may be involved in later changes in cells observed undergoing apoptosis.