Probes for Measuring Caspase Activity
Caspases (cysteine-aspartic proteases or cysteine-dependent aspartate directed proteases) are a family of protease enzymes whose functions are intimately linked with the processes of apoptosis (programmed cell death), necrosis, and pyroptosis (inflammation). AAT Bioquest offers a plethora of reagents and kits for measuring caspase activity in real-time enzyme kinetic and end-point assay formats.
What Are Caspases?
Caspases are cytosolic aspartate-specific, cysteine proteases which serve as the primary mediators of apoptosis. A variety of receptors, such as the TNF-? receptor, FasL receptor, TLR and death receptors, as well as, the Bcl-2 and inhibitor of apoptosis (IAP) protein families participate and regulate this caspase-dependent apoptosis pathway. Once activated by an upstream stimulus (extrinsic or intrinsically), caspases execute proteolysis of downstream protein substrates, triggering a ‘cascade’ of events that lead to cell disassembly, death, and the phagocytosis and removal of cellular debris.
Human Caspases
The human caspase family is divided into three main groups, primarily based on commonalities such as sequence similarity and biological function. Group 1 comprises of ‘inflammatory’ caspases with a long caspase-recruitment domain and affinity for large aromatic or hydrophobic residues at the P4 position. Group 2 comprises of ‘apoptotic effector’ caspases with a short pro-domain, while group 3 comprises of ‘apoptotic initiator’ caspases with a long pro-domain and affinity for substrates with leucine or valine at the P4 position (Table 1).
Table 1. Functional classification of human caspases.
Cell Death Pathway |
Type of Caspase |
Enzyme |
Organism |
Apoptosis |
Initiator |
Caspase 2 |
Human & Mouse |
Apoptosis |
Initiator |
Caspase 8 |
Human & Mouse |
Apoptosis |
Initiator |
Caspase 9 |
Human & Mouse |
Apoptosis |
Initiator |
Caspase 10 |
Human |
Apoptosis |
Effector |
Caspase 3 |
Human & Mouse |
Apoptosis |
Effector |
Caspase 6 |
Human & Mouse |
Apoptosis |
Effector |
Caspase 6 |
Human & Mouse |
Pyroptosis |
Inflammatory |
Caspase 1 |
Human & Mouse |
Pyroptosis |
Inflammatory |
Caspase 4 |
Human |
Pyroptosis |
Inflammatory |
Caspase 5 |
Human |
Pyroptosis |
Inflammatory |
Caspase 11 |
Mouse |
Pyroptosis |
Inflammatory |
Caspase 12 |
Some Humans & Mouse |
Pyroptosis |
Inflammatory |
Caspase 13 |
Bovine |
Chromogenic Caspase Substrates
Chromogenic caspase substrates comprise of a signal generating motif, such as the highly colored chromophore pNA (para-nitroaniline or 4-nitroaniline) linked to a caspase recognition sequence. which is monitored colorimetrically at 405 nm using either an absorbance microplate reader or a spectrophotometer.
Table 3. Chromogenic caspase substrates.
Substrate |
Target Caspase(s) |
Abs (nm) |
Color |
Unit Size |
Cat No. |
Ac-DEVD-pNA *CAS 189950-66-1* |
Caspase 3 |
405 nm |
Yellow |
5 mg |
13405 |
Z-DEVD-pNA |
Caspase 3 |
405 nm |
Yellow |
5 mg |
13422 |
Z-IETD-pNA *CAS 219138-21-3* |
Caspase 8, Granzyme B |
405 nm |
Yellow |
5 mg |
13413 |