PEPTIDYL AMMONIUM METHYL KETONES AS SUBSTRATE-ANALOG INHIBITORS OF PROLINE-SPECIFIC PEPTIDASES

Prolyl endopeptidase (PEP) and dipeptidyl peptidase IV (DP IV) are ser ine enzymes cleaving highly specific prolyl peptide bonds. Both enzyme s were found to be inhibited by newly designed peptidyl ammonium and p yridinium methyl ketones acting as slow binding inhibitors. The most p otent inhibitor of PEP is Z-Pro-Pro-CH2N+C5H5 exhibiting a K(i) value of 1.8 nM with a first-order rate constant of k(on) 0.0022 s-1 for th e formation of the tight enzyme-inhibitor complex. DP IV and H-Pro-Pro -CH2N+(CH3)3 form an enzyme-inhibitor-complex with an apparent second order rate constant of 2713 M-1 s-1. In contrast to the very stable N- terminal protected Z-Pro-Pro-CH2N+(CH3)3, the deblocked derivative dec omposes rapidly in aqueous solution.