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. 1998 Oct 5;143(1):225–239. doi: 10.1083/jcb.143.1.225

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Apoptotic extracts contain active caspases that are functionally inactivated by specific inhibitors. (A) Protocol used to prepare C/D, S/M, and E/X extracts. (B) Quantitative analysis of DEVD-AFC cleavage activity in the various extracts. DEVD-fmk treatment of S/M and E/X extracts reduces caspase activity by at least 250- and 150-fold, respectively. Note the low but nonzero level of caspase activity in the C/D extracts. Fr-3 (see Fig. 4) has ∼8% the caspase activity seen in S/M extract. Treatment of Fr-3 with DEVD-fmk further reduces this activity by ≥130-fold relative to the S/M extract. (C) Active caspases were labeled with zEK(biotin)D-aomk in S/M and E/X extracts. This labeling was completely blocked by prior incubation of extracts with YVAD-cmk and DEVD-fmk (both at 100 μM). (D) PARP and lamin A/C cleavage by caspases in the cell-free extracts is abolished after caspase inactivation with YVAD-cmk and DEVD-fmk. Note that low levels of caspases in the C/D extract cause some PARP cleavage but fail to cleave lamins.