Glycyrrhizin binding site on human serum albumin.

The binding site of glycyrrhizin (GLZ) on human serum albumin was detected through competitive displacement experiments with GLZ and ibuprofen (IBU) (diazepam site), warfarin (WAR), salicylate (SAL) (digitoxin site), or deoxycholic acid (DCA) by means of an ultrafiltration technique. The specific binding of GLZ was subject to competitive inhibition by IBU, WAR, SAL, or DCA (1 or 4 mM). The extent of displacement was in the order of: DCA greater than IBU greater than WAR greater than SAL. Conversely, the specific bindings of WAR and DCA and the low-affinity bindings of IBU and SAL were subject to competitive inhibition by GLZ (1 or 4 mM). The extent of inhibition by GLZ was in the order of DCA greater than IBU greater than WAR not equal to SAL. In addition, the low-affinity IBU binding and the specific DCA binding showed mutual competitive inhibition at 4 mM, with almost identical displacements. It was concluded that the specific GLZ binding site on human serum albumin may be located mostly within the low-affinity IBU binding site area (probably the same as the specific DCA binding site area) and partially within the specific WAR binding site area and the low-affinity SAL binding site area.