Caspase 9, apoptosis-related cysteine protease (CASP9,synonyms: MCH6, APAF3, APAF-3, ICE-LAP6, CASPASE-9c)is a member of the cysteine-aspartic acid protease (caspase) family. Sequential activation of caspases plays a central role in the execution-phase of cell apoptosis. Caspases exist as inactive proenzymes which undergo proteolytic processing at conserved aspartic residues to produce 2 subunits, large and small, that dimerize to form the active enzyme. Capase 9 is processed by caspase APAF1; this step is thought to be one of the earliest in the caspase activation cascade.