The caspases are a group of cysteine enzymes, which cleave proteins in response to intrinsic and extrinsic pathways that cause apoptotic cell death. The caspases can be grouped into two subgroups based on their roles in apoptosis. Initiator caspases (caspases 2, 8, 9, and 10) are activated through the apoptosis-signaling pathways and activate the effector caspases (caspases 3, 6, and 7) which carry out apoptosis. Caspase cascades are initiated through assembly of multiprotein complexes that trigger activation of the initiator caspases, which are then released and are able to activate the downstream effector caspases.