title: Interaction of a tricationic meso-substituted porphyrin with guanine-containing polyribonucleotides of various structures.
abstract: The interaction of a tricationic water-soluble meso-(N-methylpyridinium)-substituted porphyrin, TMPyP3+, derived from classic TMPyP4, with double-stranded poly(G)  ⋅  poly(C) and four-stranded poly(G) polyribonucleotides has been studied in aqueous buffered solutions, pH 6.9, of low and near-physiological ionic strengths in a wide range of molar phosphate-to-dye ratios (P/D). To clarify the binding modes of TMPyP3+to biopolymers various spectroscopic techniques, including absorption and polarized fluorescence spectroscopy, Raman spectroscopy, and resonance light scattering, were used. As a result, two competitive binding modes were revealed. In solution of low ionic strength outside binding of the porphyrin to the polynucleotide backbone with self-stacking prevailed at low P/D ratios (P/D  <  3.5). It manifested itself by the substantial quenching of porphyrin fluorescence. Also the formation of large-scale porphyrin aggregates was observed near the stoichiometric binding ratio. The spectral changes observed at P/D  >  30 including emission enhancement were supposed to be caused by the embedding of partially stacked porphyrin J-dimers into the polymer groove. TMPyP3+binding to poly(G) induced a fluorescence increase 2.5 times as large as that observed for poly(G)  ⋅  poly(C). In solution of near-physiological ionic strength the efficiency of external porphyrin binding was reduced substantially due to the competitive binding of Na+ions with the polymer backbone. The spectroscopic characteristics of porphyrin bound to polynucleotides at different conditions were compared with those for free porphyrin.
authors.affiliation: Department of Molecular Biophysics, B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Lenin ave, 61103 Kharkov, Ukraine. Author to whom any correspondence should be addressed.
authors.forename: Olga
authors.initials: O
authors.lastname: Ryazanova
authors.forename: Victor
authors.initials: V
authors.lastname: Zozulya
authors.forename: Igor
authors.initials: I
authors.lastname: Voloshin
authors.forename: Alexander
authors.initials: A
authors.lastname: Glamazda
authors.forename: Igor
authors.initials: I
authors.lastname: Dubey
authors.forename: Larysa
authors.initials: L
authors.lastname: Dubey
authors.forename: Victor
authors.initials: V
authors.lastname: Karachevtsev
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D006147:Guanine; D011068:Poly G; D011089:Polydeoxyribonucleotides; D011131:Polyribonucleotides; D011166:Porphyrins / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
chemical_list: D011089:Polydeoxyribonucleotides; D011131:Polyribonucleotides; D011166:Porphyrins; D011068:Poly G; D006147:Guanine