STUDIES ON THE KINETIC AND CHEMICAL MECHANISM OF INHIBITION OF STROMELYSIN BY AN N-(CARBOXYALKYL)DIPEPTIDE

We have investigated the inhibition of the human matrix metalloprotein ase stromelysin (SLN) by the N-(carboxyalkyl)dipeptide Ala[N]hPhe-leu- anilide and find that it is a competitive, slow-binding inhibitor of t his enzyme with K-i = 3 X 10(-8) M (pH 6.0, 25 degrees C). The depende nce of k(obs), the observed first-order rate constant for the approach to steady state, on Ala[N] hPhe-leu-anilide concentrations less than 10(-5) M is linear and suggests a simple, one-step mechanism with k(on ) = 3.4 X 10(4) M(-1) s(-1) and k(off) = 1.2 X 10(-3) s(-1) (pH 6.0, 2 5 degrees C). Using rapid kinetic techniques, we extended the concentr ation range of Ala[N]hPhe-leu-anilide to 2 X 10(-3) M and found that t he [Ala[N]hPhe-leu-anilide] dependence of k(obs) suggests saturation k inetics with a K-i' near 5 X 10(-4) M. Detailed analysis of these data reveal that the dependence of k(obs) on [Ala[N] hPhe-leu-anilide] is, in fact, sigmoidal. To probe the chemical mechanism of inhibition, we determined pH and temperature dependencies and solvent deuterium isot ope effects. For k(on), Delta H double dagger = 12.4 kcal/mol and -T D elta S double dagger = 6.2 kcal/mol (T = 298 K; [I](steady-state) = 10 (-6) M), while for k(off), Delta H double dagger = 12.5 kcal/mol and - T Delta S double dagger = 8.9 kcal/mol (T = 298 K). pH dependencies of the kinetic parameters for inhibition are complex but reflect greater potency at lower pH and suggest a mechanism involving the same active -site groups that are involved in catalysis. The solvent deuterium iso tope effects on k(on) are large and normal: k(on),(H2O)/k(on,D2O) = 1. 64 +/- 0.07 at pH 5.5 and 1.81 +/- 0.08 at pH 7.5. Together with the p H dependence of inhibition, these values suggest that k(on) is rate-li mited by a process that involves general-acid/general-base catalysis. We suggest that k(on) is rate-limited by general-acid-catalyzed ligand exchange of inhibitor for the zinc-bound water molecule.