Abstract
The inhibition of esterase activity of human serum albumin (HSA) by the presence of several drugs (IN) was kinetically studied assuming a scheme of competitive binding to HSA between substrate, p-nitrophenyl acetate (NPA), and IN. The IN included N-arylanthranilic acids, coumarin derivatives and prostaglandins. The conditions of excessive concentrations of HSA and IN compared with NPA were employed to avoid complexities due to multiple active sites of HSA. For the solubilization of IN some organic solvents were added and the effects of the solvents on the reaction parameters of NPA with HSA were investigated. The dissociation constants of IN-HSA complexes were determined from the double reciprocal plots based on the scheme. The bulkiness of the substituents on phenyl groups of N-arylanthranilic acids enhanced the inhibition. Warfarin did not inhibit the reaction at all. Prostaglandins showed rather little inhibitions. From the comparisons of the dissociation constants obtained from this kinetic method with the literature binding constants from the conventional static methods, it was suggested that the esterase active site differed from the conventional binding sites on HSA.
