THE KINETIC MECHANISM OF INHIBITION OF HUMAN-LEUKOCYTE ELASTASE BY MR889, A NEW CYCLIC THIOLIC COMPOUND

The cyclic thiolic compound 2-[3-thiophencarboxythio]-N-[dihydro-2(3H)-thiophenone1-3-il]-propionamide (MR889) was investigated as inhibitor of endopeptidases. The activity of bovine pancreatic α-chymotrypsin, human leukocyte cathepsin G and rabbit liver cathepsin B was not affected by MR889, whereas porcine pancreatic elastase and human leukocyte elastase were inhibited. The kinetic mechanism of inhibition of human leukocyte elastase was of the reversible, slow-binding, fully competitive type. The rate constants for complex formation between MR889 and leukocyte elastase, determined by pre-steady-state kinetic analysis in the presence of a tetrapeptide substrate at 37° and pH 7.40, were kon = 2363 ± 15 M-1 sec-1, koff = 3.01 ± 0.34 × 10-3 sec-1. The inhibition equilibrium constant was ki = koff kon = 1.27 ± 0.15μM. Ki, calculated from steady-state kinetic experiments, was 1.38 μM. MR889 also inhibited the elastolytic activity of leukocyte elastase, as determined with insoluble elastin as the substrate. © 1990.