The interaction of 8-anilino-1-naphthalenesulfonate with polylysine and polyarginine

Comparative studies on the interaction of 8-anilino-1-naphthalenesulfonate (ANS) with polylysine and polyarginine have been made by equilibrium dialysis and fluorescence or circular dichroism measurements, to investigate the structural characteristics of the polypeptides. The results are summarized as follows: (i) ANS binds to either of the polypeptides primarily by electrostatic interaction while hydrophobic interaction partially facilitates the dye binding; both interactions are stronger in the polyarginine-dye binding than the polylysine-dye binding. (ii) The fluorescence of ANS is more intensified when the dye binds to polyarginine than to polylysine regardless of the value of r (number of bound dye per amino-acid residue) of polypeptide-dye complexes, although the intensification depends on the r value and becomes maximum at r = 0.25–0.35 for both cases. (iii) The binding of ANS to each polypeptide is cooperative at r < 0.4. (iv) The circular dichroism is more efficiently induced in the spectral region of ANS by binding to polyarginine than to polylysine. From these results, it was concluded that, compared to polylysine, polyarginine suffers some structural change by ANS binding into a more compact molecular configuration having some regularity with a lower dielectric environment.