Circular dichroism of complexes between acetylated poly-L-lysine and deoxyribonucleic acid.

Poly-l-lysine (poly(Lys)) was acetylated to various extents and the conformation of the polypeptide with different degrees of acetylation was studied by using the circular dichroism (CD) technique. It was found that by increasing the percent of acetyl groups in the side chain, the polymer assumes an increasing percent of α-helix conformation. The CD of complexes between acetylated poly(Lys) and deoxyribonucleic acid (DNA) was also studied. The effect due to the polypeptide on the optical properties of nucleic acid in the region 245-300 nm, at a constant ratio of neutralization, decreases by increasing the percent of acetylation. Comparison with the CD spectra of DNA-poly(Lys) complexes at different ratios of neutralization suggests that the same type of perturbation on the electronic transitions of DNA is involved. The optical properties of DNA are not influenced by the polypeptide α-helical regions, whereas these regions are involved in the complex formation according to the results of the thermal stability of the complex.