Optical studies on interaction of biliary contrast agents with native and modified human serum albumin

The interaction of two homologous series of biliary contrast agents with native human and bovine serum albumin and with modified human serum albumin was investigated using circular dichroism and equilibrium dialysis. For most derivatives, extrinsic Cotton effects were observed for the interaction with both albumins. In some cases, these effects were strongly affected by only small changes in the chemical structure of the drugs. These large differences in extrinsic Cotton effects can be explained by definite effects of the chemical structures on the binding site selectivity of some drugs. For example, iopodate preferentially binds to the warfarin binding site of human serum albumin, while an ethyl group into the propionic acid side chain reduces the affinity for the warfarin site but strongly increases the affinity for the diazepam binding site of human albumin.