N-PEPTIDYL, O-ACYL HYDROXAMATES - COMPARISON OF THE SELECTIVE-INHIBITION OF SERINE AND CYSTEINE PROTEINASES

Two series of N-aminoacyl, O-benzoyl hydroxamates were designed to inv estigate the influence of the substituted benzoyl residue on the hydro lytic stability and the reactivity of these potential inhibitors towar ds selected cysteine and serine proteinases. The inactivators react mo re rapidly with cysteine proteinases than with the serine enzymes test ed, While Z-Phe-Gly-NHO-Nbz is the most reactive inhibitor of cathepsi n L, inhibiting the target protein by a second order rate constant of 932.000 M(-1) s(-1), the bacterial serine proteinase thermitase is inh ibited best by Z-Gly-Phe-NHO-Nbz, exhibiting a second-order rate const ant of 1.170 M(-1) s(-1). Thiolsubtilisin, having the thiol-group as t he reactive nucleophile instead of serine, exhibits specificity consta nts of the inactivation two orders of magnitude smaller than subtilisi n. The degree of selectivity of the inhibitors relative to cathepsin B , cathepsin L, cathepsin S and papain varies up to two orders of magni tude with respect to their second order rate constant of inactivation. The inhibitory reactivity of these compounds varies only up to sixfol d depending on the benzoyl substituent. Similarly, the rate constants for the hydrolytic decomposition of the compounds vary by a factor of about 6, suggesting that the structural and mechanistic features of th e compounds which are responsible for decomposition as well as for the enzyme inhibition are the same. Comparing both reactions, the data al low the calculation of an acceleration factor of 2.4 x 10(10) for the inhibition of cathepsin L by its most effective inhibitor, clearly cha racterizing this enzyme inhibition reaction as enzyme-activated.