Absorption and Fluorescence Characteristics of the Binding of Ethidium Bromide with Synthetic Single- and Double-Stranded Polyribonucleotides

A comparative study of the complex formation of ethidium bromide (EtBr) and methylene blue (MB) with synthetic single-stranded (ss-) polynucleotides poly(rA) and poly(rU) was conducted. The absorption spectra of these ligands decreased upon interaction with ss-polynucleotides and poly(rA)-poly(rU) formed at their hybridization. In the case of the MB-polynucleotide complexes, the fluorescence intensity decreases, while in the case of EtBr, the fluorescence intensity increases along with the enhancement of concentrations of polynucleotides. Based on the fluorescence spectra analysis of the complexes EtBr with ss- and hybrid ds-polynucleotides, the binding curves in Scatchard coordinates were constructed (r/C_f and r), and the values of the binding parameters of polynucleotides determined, including the binding constant value K and the number of bases n (base pairs at hybridization) per binding site..