Hu. Demuth et al., N-PEPTIDYL, O-ACYL HYDROXAMATES - COMPARISON OF THE SELECTIVE-INHIBITION OF SERINE AND CYSTEINE PROTEINASES, Biochimica et biophysica acta. Protein structure and molecular enzymology, 1295(2), 1996, pp. 179-186
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.