Effects of drug binding on the esterase-like activity of human serum albumin. III. Evaluation of reactivities of the two active sites by using clofibric acid as an inhibitor.

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Abstract
The reactivities of the 2 esterase-like active sites on human serum albumin (HSA) towards p-nitrophenyl acetate (NPA) were evaluated in pH 7.4 phosphate buffer (.mu. = 0.2) and at 25.degree. C. Clofibric acid (CA) was used to distinguish between the 2 sites, the primarily reactive site (R site) being inhibited by CA and the secondarily reactive site (T site) not inhibiited by CA. The kinetic parameters for the 2 sites were determined. The dissociation constant between CA and R site of HSA determined kinetically was consistent with the reciprocal of the binding constant obtained from the equilibrium dialysis experiment. The contribution of the T site to the overall activities of HSA was estimated from the specificity constants (the ratio of the catalytic rate constant to the dissociation constant) and was 11.1%.