Light absorption and CD spectra of bound bilirubin and albumin fluorescence spectra have been recorded from mixtures containing albumin, A, bilirubin, B, and laurate, L, in Tris-NaCl buffer at pH 8.2, 25 degrees C. Concentrations of the corresponding stoichiometric complexes, ABiLj, for i = 0/3 and j = 0/3, have been calculated from previously determined stoichiometric cobinding constants (H. Sato et al. (1988) Arch. Biochem. Biophys. 260, 811-821). Spectral data of the complexes have finally been found by iterative computer fitting using the principle of several acceptable solutions (R. Brodersen et al. (1987) Eur. J. Biochem. 169, 487-495). The results were utilized at the microscopic level to investigate ligand-induced conformational changes. When laurate was bound to AB, a decrease of the distance between Trp-214 and the bound bilirubin occurred, as measured according to Förster's principle. The distances were 21.9 +/- 0.3 A in AB, 19.7 +/- 0.3 A in ABL, and 17.9 +/- 0.2 A in ABL2.