On the contemporaneous, reversible interaction of different ligands with serum albumins in dilute aqueous solutions. Fluorescein and phenylbutazone.

The binding affinity of fluorescein and of phenylbutazone to human serum albumin (HSA) and to bovine serum albumin (BSA), respectively, as well as of the two drugs together to each protein in dilute aqueous solution has been studied by means of gel permeation chromatography, circular dichroism, U.V. absorption and fluorescence spectroscopy. Identity of and/or interdependence between primary binding sites for the two ligands considered on HSA and BSA are evidenced and correlated with a simple theoretical approach to mixed drugs binding.