ABSORPTION AND EMISSION SPECTRAL STUDIES OF BILIRUBIN IX-ALPHA COMPLEXES WITH SODIUM TAUROCHOLATE IN AQUEOUS BUFFER, PH 8.0

The absorption and fluorescence emission properties of (4Z,15Z)-biliru bin IXalpha and xanthobilirubic acid in aqueous buffer at pH 8.0 and i n the presence of the bile salt sodium taurocholate in the concentrati on range 1-40 mmol dm-3 have been measured. The results are consistent with the formation of a complex in which an intramolecularly hydrogen -bonded conformer of bilirubin is bound in a hydrophobic microenvironm ent of a taurocholate aggregate, and in which molecular rotations and vibrations of the pigment are relatively unrestrained.