CHARACTERIZATION OF THE DIHYDROXY BILE-SALT BINDING-SITES ON BOVINE SERUM-ALBUMIN

The binding of hydroxy bile salts to bovine serum albumin was studied using various probes such as: dansylamine (probe for site I), dansylsarcosine (probe for site II), coumarin (probe for site III) and danyslated albumin (probe for bilirubin binding site). The bile salt-albumin complex formation was entropically driven, assoicated to an enthalpic-entropic compensation effect due to the water molecules participation in the interaction. Only tryptophan 134 residue of the albumin was accessible to these ligands. The hydroxyl in position C-7 in the steroid ring plays an important role in the interaction. The presence of a lysine 195 residue at the binding sites for bile salts is demonstrated. A low ligand to protein ratio all the bile salts inhibit the binding to the site II marker and produce a perturbation at the site I and III of the albumin. It is suggested that site II is overlapping with the site I and III.