Binding and circular dichroism data on bilirubin-albumin in the presence of oleate and salicylate

Abstract

The binding of equimolar amounts of bilirubin to human and bovine serum albumin in 0.1 phosphate buffer, pH 7.4, in the presence and absence of various concentrations of oleate or salicylate was studied by the use of an ultracentrifugal technique. The resultant data showed salicylate to be a poor competitor for the bilirubin binding sites; in the presence of a considerable excess of salicylate, only small amounts of bilirubin were liberated from the proteins. The dissociation of bilirubin from albumin by oleate was very dependent on the oleate concentration. No bilirubin was liberated from the proteins at oleate:albumin molar ratios below 5. All the bilirubin was liberated from the proteins at oleate:albumin molar ratios above 8.Marked changes in the absorption and circular dichroism spectra of the bilirubin-albumin solutions were observed on the addition of salicylate or oleate even under conditions in which little or no bilirubin was liberated from the proteins. While the binding characteristics and absorption spectra of the human and bovine albumin-bilirubin complexes in the presence and absence of oleate or salicylate were very similar, the Cotton effects generated by the addition of bilirubin to the human albumin were very different from those obtained with the bovine protein.