The caspase family of cysteine proteases play a key role in apoptosis. Caspase-3 is the most extensively studied apoptotic protein among caspase family members. Caspase-3 is synthesized as inactive pro-enzyme that is processed in cells undergoing apoptosis by self-proteolysis and/or cleavage by another upstream protease. The processed form of caspase-3 consists of large (17 kD) and small (12 kD) subunits which associate to form an active enzyme. The active caspase-3 proteolytically cleaves and activates other caspases, as well as relevant targets in the cells (e.g., PARP and DFF).