Quantitative structure-activity relationships for the pre-steady state of Pseudomonas species lipase inhibitions by p-nirophenyl-N-substituted carbamates

摘要

The pre-steady states of Pseudomonas species lipase inhibitions by p-nitrophenyl-N-substituted carbamates (1-6) are composed of two steps: (1) formation of the non-covalent enzyme-inhibitor complex (E:I) from the inhibitor and the enzyme and (2) formation of the tetrahedral enzyme-inhibitor adduct (E-I) from the E:I complex. From a stopped-flow apparatus, the dissociation constant for the E:I complex, K-S, and the rate constant for formation of the tetrahedral E-I adduct from the E:I complex, k(2) are obtained from the non-linear least-squares of curve fittings of first-order rate constant (k(obs)) versus inhibition concentration ([I]) plot against k(obs)=k(2)+k(2)[I]/(K-S+[I]). Values of pK(S), and log k(2) are linearly correlated with the rho(*) values with the rho(*) values of -2.0 and 0.36, respectively. Therefore, the E:I complexes are more positive charges than the inhibitors due to the rho(*) value of -2.0. The tetrahedral E-I adducts on the other hand are more negative charges than the E:I complexes due to the rho(*) value of 0.36. Formation of the E:I complex from the inhibitor and the enzyme are further divided into two steps: (1) the pre-equilibrium protonation of the inhibitor and (2) formation of the E:I complex from the protonated inhibitor and the enzyme.