The induced circular dichroism of bilirubin complexed with the alpha-helix form of poly(L-lysine).

Binding of bilirubin by the alpha-helix conformation of poly(L-lysine) in water induces optical activity. The bisignate circular dichroism spectrum exhibits exciton bands centred at 444 nm, negative, and at 525 nm, positive. The magnitude of the induced circular dichroism depends on the concentration of total bilirubin and total lysine residues, the molar ratio of total lysine residues-to-total bilirubin molecules, the pH and the degree of polymerization of poly(L-lysine). Although bilirubin binds to the random coil conformation of poly(L-lysine), as evidence by the absorption spectrum, the complex is optically inactive. The results suggest that bilirubin binds to the poly(L-lysine) in the form of dimers and oligomers.