Cell experiment:

For the detection of caspase-3 activity, PBS washes cell pellets (derive from either the medium or the adherent cells) which are suspended in extract buffer [25 mM HEPES (pH7.4), 0.1% TritonX-l00, 10% glycerol, 5 mM DTT, 1mM phenylmethylsulfonyl fluoride, 10 mg/mL pepstatin, and 10 mg/mL Leupeptin] and vortexed vigorously. 20μl of extract (corresponding to 10% of the sample) are incubated with the caspase-3 fluorogenic substrates Ac-DEVD-AFC at 100 μM final concentration at room temperature, and caspase-3 activity is measured continuously by monitoring the release of fluorigenic AFC at 37℃[1].

Ac-DEVD-AFC is a fluorogenic substrate for activated caspase-3 (CPP32) with Km value of 9.7 μM, and related cysteine proteases [1][2].

Apoptosis is a process of programmed cell death that occurs in multicellular organisms. Caspase are a family of protease enzymes playing essential roles in programmed cell death (including apoptosis, pyroptosis and necroptosis) and inflammation. Caspase activation is a major event in apoptosis. Caspase-3 cleaves and activates caspases 6 and 7, and is processed and activated by caspases 8, 9, and 10 [1][2][3].

Ac-DEVD-AFC (N-Acetyl-Asp-Glu-Val-Asp-7-amido-4-Trifluoromethylcoumarin) is a fluorogenic substrate for activated caspase-3 and related caspases. During apoptosis, activated caspase-3 cleaves poly (ADP-ribose) polymerase, which it specifically targets at the amino sequence Asp-Glu-Val-Asp (DEVD). Sequence is based on PARP cleavage at Asp216 for caspase-3 [1][2]. Caspase activity can be quantified by fluorescent detection of free AFC (7-amino-4-trifluoromethylcoumarin) at excitation 400 nm and emission 505 nm [2].

References:
[1].  Lazebnik YA1, Kaufmann SH, Desnoyers S, et al. Cleavage of poly(ADP-ribose) polymerase by a proteinase with properties like ICE. Nature. 1994 Sep 22;371(6495):346-7.
[2].  Xiang, J.,Chao, D.T., and Korsmeyer, S.J. BAX-induced cell death may not require interleukin 1β-converting enzyme-like proteases. Proceedings of the National Academy of Sciences of the United States of America 93, 14559-14563 (1996).