  Binding of anthracycline antibiotic carminomycin (CM) to synthetic
polyribonucleotides poly(A) and poly(U) was studied in solution of low ionic
strength in a wide phosphate-to-dye (P/D) range using absorption and polarized
fluorescence spectroscopy. Two different modes of CM binding to the
ss-polynucleotides have been identified. The first of them dominating at low
phosphate-to-dye (P/D) ratios is self-assembly of the heterocyclic dye on the
polymer surface driven by to cooperative electrostatic binding of amino group
of CM sugar moiety to negatively charged polynucleotide phosphate groups with
the chromophores self-stacking. At high P/D values, the stacking-associates
disintegrate and monomeric binding of ligand to nucleic bases become prevalent.
Thermodynamic parameters of binding were estimated for the both cases.
