Effect of Modification of Albumin on Tolbutamide-Serum Albumin Binding

Abstract

The binding of tolbutamide, a representative sulfonylurea-related drug, to bovine serum albumin (BSA) modified completely or partially with three chemicals (p-chloromercuribenzoic acid, p-aminophenylmercuric acetate and p-hydroxynitrobenzyl bromide) was investigated by means of an equilibrium dialysis method. Scatchard plots of the data indicated that : (1) free sulfhydryl groups in the BSA molecule are not important binding sites for tolbutamide, (2) two tryptophan residues in the BSA molecule form a hydrophobic region, (3) one of the two tryptophan residues in the BSA molecule may be related to the binding of tolbutamide. These results are discussed in relation to the mechanisms responsible for the binding of sulfonylurea-related compounds to serum albumin.