Effects of drug binding on the esterase-like activity of human serum albumin. IV. Application of an analog computer to determination of the multiple dissociation constants.

Publisher Website
Google Scholar
Abstract
The inhibition parameters of various drugs (inhibitor, I) for the reaction of p-nitrophenyl acetate (substrate, S) with human serum albumin (HSA) could not be directly determined, because HSA has 2 esterase-like active sites for S (i.e., R and T sites) and 3 drug binding sites (i.e., R, T and U sites). Kd between I and the individual binding sites on HSA, KI,R, KI,T and KI,U, were determined by analog computer simulation of the inhibition. Clofibric acid, ibuprofen and dansylsarcosine bound solely to the R site, and their KI,R values were determined. Flufenamic acid, ethacrynic acid and salicyclic acid bind primarily to the R site and then to the T site, and their KI,R and KI,T values were estimated. The KI,U and KI,R values for phenylbutazone and sulfinpyrazone were also determined, and their KI,U values were smaller than their KI,R values. It is likely that warfarin binds primarily to 2 binding sites unconcerned with the esterase-like activities and then to the R site of HSA, and these 3 Kd were estimated. Since this kinetic method distinguishes the drug binding sites on HSA and gives the Kd for the individual sites, it is very useful for studies on drug interaction with HSA.