Effects of a perfluorochemical emulsion on L-tryptophan binding by human albumin

The effect of a perfluorochemical emulsion on ligand binding by human albumin was studied using a site specific approach. L-tryptophan was used as a marker for binding to site II on human albumin. Centrifugation, followed by supernatant ultrafiltration at ambient room temperature, was employed to determine the per cent tryptophan free. The partitioning of tryptophan from pH 7.4 phosphate buffer into the pure perfluorochemical liquids was insignificant. Tryptophan was not significantly bound by the perfluorochemical emulsion droplets. Binding of tryptophan by buffer dilutions of human albumin demonstrated that, at the tryptophan concentrations examined, human albumin concentration had little effect on the per cent tryptophan free. Tryptophan binding by mixtures of the perfluorochemical emulsion and human albumin showed that, at sufficiently high concentrations of the perfluorochemical emulsion, one or more of the emulsion components is responsible for the direct and/or indirect displacement of human albumin-bound tryptophan. The individual perfluorochemical emulsion components were studied for their effects on the binding of tryptophan by human albumin. Results showed that oleic acid and, to a very small degree, Pluronic F-68, were responsible for the displacement of human albumin-bound tryptophan.