During apoptosis, activated caspase-3 cleaves several substrates, including poly(ADP-ribose) polymerase, which it specifically targets at the amino sequence DEVD. Ac-DEVD-pNA is a para-nitro aniline chromophore cleaved by caspases (Km = 18, 11, 32, 180, and 12 礛 for caspases-1, -3, -4, -6, and -7, respectively). It is not cleaved by caspase-2.2 Cleavage is monitored colorimetrically at 405 nm