Hi,

this is entirely possible and rather depends on your antibody. Some antibodies preferentially detect the newly exposed N-terminus of cleaved caspase. However, bear in mind that cleaved caspase-4 is not necessarily active, since caspase-4 (like all caspases with a long pro-domain) requires dimerization for activation while outside proteases can cleave the inactive caspase. If you want to make sure your caspase is active, you should try to label it with an activity based probe such as biotinylated VAD. Matt Bogyo's lab also developed one specifically for the inflammatory caspases, AWP28: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3461347/ It's fluorescent and works nicely. I'm sure they'd be happy to share some with you.

Also, bear in mind that caspase-4 is almost identical to caspase-5 so your antibody likely won't differentiate between those two.

1) Don't expect anti-body to work everytime

2) The smaller subunit is 10kD it might have run out, you can try using higher concentrated gel or shorter run time.

3) For procaspase (refer to point 1 but it also) could be exposure time is not enough. If the cell in your control is still alive then it could be either.

BUT if you read the reference from Santa Cruz, the subunit at 43KD is the p20 subunit... (just like p53 is not 53kD maybe) so be sure of the position where you are looking for your protein

thank you for your responses, but I am working with Anti-Caspase 4 antibody (ab22687). the Datasheet of this antibody mentioned  that it recognises proenzyme (43 kDa) and the large subunit (19 kDa) and small (10 kDa) subunits of mature enzyme. For the mature enzyme, reactivity is strongest with the large subunit. No cross reactivity with other human caspases tested (1 to 3, 5 to 10, 14).