Inhibition of human pancreatic elastase 2 by peptide chloromethyl ketones

Abstract The inactivation of human pancreatic elastase 2 (EC 3.4.21.11) by a series of peptide chloromethyl ketones has been investigated. Among a series of compounds with the structure X-Ala-Ala-Pro-Y-CH 2 Cl (were X = acetyl-, succinyl-, methylsuccinyl-, or H- ), the kinetic parameters for inhibition of elastase 2 depend markedly on the amino acid (Y) in the P1 position. Succinyl-Ala-Ala-Pro-Leu-CH 2 Cl was found to be an extremely effective inhibitor of human elastase 2, with a first-order rate constant for covalent bond formation ( k 3 ) of 0.033 s −1 and a dissociation constant, K i , for the enzyme inhibitor complex of 7.4 · 10 −7 M . The second-order rate constant k 3 /K i for inhibition of elastase 2 by the analogous compound containing a free amino group in place of the succinyl moiety is 150 times lower than that found for the succinyl or acetyl derivative, suggesting that the presence of a positive charge at this position reduces the proper binding of the inhibitor to the enzyme.