Activation and function of caspases in apoptosis

Caspases are the key executioners of apoptosis. Up to now at least 14 mammalian caspases have been identified. Caspases are synthesized as zymogens that have very low catalytic activity. The zymogens can be activated and active caspases specifically cleavage a set of substrates and then lead to apoptosis. There are at least three distinct apoptosis pathways involved in caspases: mitochondrial/cytochrome C, death-receptor and endoplasmic reticulum-mediated apoptosis pathways. Caspases and their inhibitors always coexist lest that caspases are activated accidentally and hurt the normal cells.