pNA (4-nitroaniline)-derived caspase substrates are widely used for the colorimetric detection of various caspase activities. Cleavage of pNA peptides by caspases generates pNA that is monitored colorimetrically at ~405 nm. pNA has maximum absorption around 408 nm. Caspase-1 substrate with Km = 18 uM and kcat = 0.5 M-1s-1; Caspase-3 substrate with Km = 11 uM and kcat = 2.4 M-1s-1;Caspase-4 substrate with Km = 32 uM and kcat = 0.05 M-1s-1 Caspase-6 substrate with Km = 180 uM and kcat = 0.6 M-1s-1 ; Caspase-7 substrate with Km = 12 uM and kcat = 0.4 M-1s-1; Caspase-8 substrate with Km = 167 uM
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