INTERACTION OF METHYLENE BLUE WITH SINGLE-STRANDED POLYNUCLEOTIDES POLY(rA) AND POLY(rU) AND WITH DOUBLE_STRANDED POLYNUCLEOTIDE POLY(rA)-POLY(rU)

Abstract

Interaction of dye-intercalator methylene blue (MB) with single-stranded (ss-) polynucleotides poly(rA), poly(rU) and double-stranded poly(rA)-poly(rU) has been studied by the method of absorption spectroscopy at various concentration ratios ligand/phosphate (concentration of ss-polynucleotides by phosphate residue). It was revealed that in the absorption layer of methylene blue, in the wavelength change interval 500≤λ≤750 nm, the absorption spectra of the complexes MB-ss-poly(rA) decrease more sharply, as compared to MB spectrum, along with polynucleotide concentration enhancement in the solution. It was also revealed that the absorption spectra of the complexes MB-ss-poly(rU) decrease moderately at the increase of this polynucleotide concentration in the solution. In the spectra of the complexes MB-ss-poly(rU) a pseudo-isosbestic point is formed, while in the spectra of the complexes MB-ss-poly(rA) there is no such point. The pseudo-isosbestic point is formed also in the spectra of the complexes MB-poly(rA)-poly(rU). It was also revealed that the absorption spectra of the complexes of MB with ss-poly(rA) and poly(rA)-poly(rU) are shifted to the longer wavelengths by ~5-7 nm, while the shift in the absorption spectra of the complexes MB-ss-poly(rU) composes almost ~2 nm. The absorption spectra changes of the complexes of MB with the mentioned polynucleotides indicate that MB shows higher specificity to poly(rA), as compared to poly(rU) and poly(rA)-poly(rU). The obtained data also indicate that MB binds to poly(rA) and poly(rA)-poly(rU) by intercalation and electrostatic modes, and with ss-poly(rU) – mainly by electrostatic mechanism.