BINDING-SITES OF FLUORESCENT-PROBES ON HUMAN SERUM-ALBUMIN

Human serum albumin is known to have two major and selective drug bind ing sites, termed sites I and II. The fluorescent probes, dansylamide and dansylsarcosine selectively interact with sites I and II, respecti vely. However, the binding site of the fluorescent probe dansylglycine on human serum albumin is not clear from the literature. This study i nvestigated whether dansylglycine interacts tightly with site I or II. Spectrofluorimetric titrations (quenching and complex) and circular d ichroism measurements were performed to determine the binding characte ristics of dansylglycine to human serum albumin. Modification in probe fluorescence was described by fluorescence titrations to be a result of competitive displacement by ligands. The pattern of displacement of this probe by several ligands whose primary binding sites are exactly known, enabled the identification of its specific binding site. The f luorescence of dansylglycine is only extensively changed when ligands of site II are added, suggesting that it strongly interacts with the b enzodiazepine/indole binding site on human serum albumin.