POTENT INACTIVATION OF CATHEPSIN-S AND CATHEPSIN-L BY PEPTIDYL (ACYLOXY)METHYL KETONES

Peptidyl (acyloxy)methyl ketones (Z-Aa-Aa-CH2-OCO-R), a new class of i rreversible inhibitors whose chemical reactivity can be modulated by v arying the substitution pattern of the carboxylate leaving group, are shown to be extremely potent inactivators of the lysosomal cysteine pr oteinases cathepsin L and cathepsin S. The highest k(2)/K-i values mea sured were found to exceed 10(6) M-ls-l for both cathepsin i, and cath epsin S. The rate of inactivation can be controlled by varying the dip eptidyl moiety or the carboxylate leaving group, with the second-order rate constants for both enzymes found to be strongly dependent on the p K,values of the leaving group. The specificities of the cathepsins S and L reveal a different selectivity towards the nature of substitut ion of the aryl P' leaving group of the inhibitor. This new inhibitor class opens the possibility of the design of selective and specific in hibitors for lysosomal cysteine proteinases.