The caspase-9 antibody 3-20 recognizes caspase-9, a member of the cysteine-aspartic acid protease (caspase) family. It is widely expressed and is particularly important during development. Human pro-caspase-9 is a 46 kDa, 416 amino acid (aa) protein and contains one CARD region (aa 192) and catalytic residues at His237 and Cys287. 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 two subunits, large and small, that dimerize to form the active enzyme. This protein can undergo autoproteolytic processing and activation by the apoptosome, a protein complex of cytochrome c and the apoptotic peptidase activating factor 1; this step is thought to be one of the earliest in the caspase activation cascade. The caspase 9 protein is thought to play a central role in apoptosis and to be a tumor suppressor. Alternative splicing results in multiple transcript variants.