Specific and non-specific ligand binding to serum albumin

The applicability of a model of specific and non-specific bincling sites for the bincling of organic ligands to serum albumin was examined statistically. It is proposed in this model that there are a limited number of a single class of high affinity sites and an unlimited number of low affinity sites. Ligands bind to the former sites independently, as in the Scatchard model for a single class of bincling sites, and to the latter sites in a partition-like manner, the amounts bound increasing linearly with the concentration of free ligands. In this study, data on the bincling of warfarin to human serum albumin reported by Wilting et al. [J. Wilting et al., J. biol. Chem.255, 3032 (1980)] and on the binclings of indomethacin and salicylic acid to human serum albumin reported by Hultmark et al. [D. Hultmark et al., Acta pharm. suecica12, 259 (1975)] were used. These bincling data were analyzed accorcling to the model of specific and non-specific sites as well as the Scatchard model of two classes of bincling sites. Statistical analyses showed that the model of specific and non-specific bincling sites fitted the data for bincling of all compounds very well, indicating the applicability of this model. An index of the upper limit of ligand concentrations necessary for accurate analysis of the bincling data was also discussed.