Non-specific effects of methyl ketone peptide inhibitors of caspases

Caspases are a family of cysteine proteases which play a crucial role in ap optosis and inflammation. The involvement of caspases in these processes ca n be demonstrated by their irreversible inhibition with fluoromethyl ketone and chloromethyl ketone derivatives of peptides resembling the cleavage si te of known caspase substrates, These inhibitors irreversibly alkylate the cysteine residue in the active site of caspases, In this study we show that a biotinylated fluoromethyl ketone peptide inhibitor of caspases (z-VAD,fm k) also efficiently affinity-labeled cathepsin B and cathepsin H, In additi on, the caspase inhibitors z-VAD.fmk, z-DEVD.fmk and Ac-YVAD.cmk also effic iently inhibited cathepsin B activity in vitro and in tissue culture cells at concentrations that are generally used to demonstrate the involvement of caspases, (C) 1999 Federation of European Biochemical Societies.