Analysis of the Circular Dichroism of the Complexes of 8-Anilino-1-naphthalenesulfonate with Bovine Serum Albumin

The induced circular dichroic (CD) spectra of anilinonaphthalenesulfonate bound to bovine serum albumin were resolved into four component rotational transitions. The change in the CD spectrum with the average number of bound ligands is shown to involve only two of the component bands and is attributed solely to coupling of transitions in the bound anilinonaphthalenesulfonate molecules. Under conditions of stoichiometric binding, the observed CD spectra could be represented as a superposition of two basic spectral components, one resulting from interaction of the ligand with the protein and the other from a pairwise interaction of bound ligands. The interpretation of the findings is consistent with the presence of essentially equivalent binding sites for anilinonaphthalenesulfonate on albumin, a conclusion obtained previously from direct fluorimetric titrations.