The caspases, comprising a family of cysteine proteases, have been firmly established as major mediators of the execution phase of apoptosis. While most of the known CASPs are involved in apoptosis, others function as proinflammatory caspases, leading to the maturation of proinflammatory cytokines. Cross-linking of death receptors (TNFR1, Fas, and death receptor 3) can directly activate caspases, whereas most other apoptotic stimuli lead to mitochodnrial changes and a subsequent activation of the caspase cascade. 

Caspases have cysteine at their active site and cleave target proteins at specific aspartic acids.  All caspases share similarities in amino acid sequence. They are expressed as proenzymes that contain 3 domains; an N-terminal prodomain, a large subunit containing the active site cysteine and a C-terminal small subunit. Processing of caspases to a mature product occurs following different apoptotic stimuli, and requires cleavage at specific aspartic acid residues located between the different subdomains. Two types of proteases have been shown to perform this type of aspartic acid specific maturation: the caspases themselves and the serine protease granzyme B. 

Once activated, caspases cleave and thereby activate other procaspases, resulting in an amplifying proteolytic cascade. Some of the activated caspases then cleave other proteins in the cell like nuclear lamins and a protein that normally holds a DNAse in an inactivative form thereby paving the way for the DNAse to cut up the DNA in the cell nucleus. 

–Caspase 3 activation is said to be a critical initial event in the apoptosis enactment caspase cascade. In this cascade, cytochrome c, normally sequestered in the mitochondrial intermembrane space, is released through the mitochondrial outer membrane early during apoptosis and interacts with Apaf-1, dATP (or ATP), and procaspase 9, culminating in the proteolytic activation of the caspase 9 zymogen. Activated caspase 9 activates procaspase 3, and caspase 3, in turn, activates a DNA fragmentation factor (DFF)/caspase-activated DNase (CAD), which finally induces DNA fragmentation. 

—Inhibitors of Caspases

• Viral inhibitors of caspases: Several viruses encode proteins which inhibit caspases.

• p21 has been reported to inhibit caspase 3

Apaf-1: is a cell-death effector that acts with cytochrome c and caspase-9 to mediate p53 dependent apoptosis. It is a potential tumor suppressor.

Cytochrome c is normally sequestered in the mitochondria, but it is released into the cytosol on treatment with certain apoptotic stimuli. There, cytochrome c triggers oligomerization of Apaf-1, which then binds and activates Casp9. 

Caspase 12: is polymorphic which means that its sequence varies in different people.