Tripeptidyl peptidase II (TPPII) is a serine peptidase of the subtilisin-type which removes tripeptides from the free NH2 terminus of oligopeptides. AAF-CMK is an irreversible inhibitor of TPPII commonly used at 10-100 μM. It does not significantly interfere with the chymotrypsin-like activity of the proteasome. AAF-CMK also inhibits bleomycin hydrolase and puromycin-sensitive aminopeptidase when used at 50 μM.