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Phase equilibrium in poly(rA) · poly(rU) complexes with Cd 2+ and Mg 2+ ions, studied by ultraviolet, infrared, and vibrational circular dichroism spectroscopy
Author(s) -
Blagoi Yurii,
Gladchenko Galina,
Nafie Laurence A.,
Freedman Teresa B.,
Sorokin Victor,
Valeev Vladimir,
He Yanan
Publication year - 2005
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.20288
Subject(s) - chemistry , circular dichroism , crystallography , infrared spectroscopy , absorption (acoustics) , polynucleotide , absorption spectroscopy , spectroscopy , analytical chemistry (journal) , materials science , biochemistry , physics , organic chemistry , chromatography , quantum mechanics , composite material
Ultraviolet (UV) and infrared (IR) absorption and vibrational circular dichroism (VCD) spectroscopy were used to study conformational transitions in the double‐stranded poly(rA)· poly(rU) and its components—single‐stranded poly(rA) and poly(rU) in buffer solution (pH 6.5) with 0.1 M Na + and different Mg 2+ and Cd 2+ (10 −6 to 10 −2 M ) concentrations. Transitions were induced by elevated temperature that changed from 10 up to 96°C. IR absorption and VCD spectra in the base‐stretching region were obtained for duplex, triplex, and single‐stranded forms of poly(rA) · poly(rU) at [Mg 2+ ],[Cd 2+ ]/[P] = 0.3. For single‐stranded polynucleotides, the kind of conformational transition (ordering → disordering → compaction, aggregation) is conditioned by the dominating type of Me 2+ –polymer complex that in turn depends on the ion concentration range. The phase diagram obtained for poly(rA) · poly(rU) has a triple point ([Cd 2+ ] ∼ 10 −4 M ) at which the helix–coil (2 → 1) transition is replaced with a disproportion transition 2AU → A2U + poly(rA) (2 → 3) and the subsequent destruction of the triple helix (3 → 1). The 2 → 1 transitions occur in the narrow temperature interval of 2°–5°. Unlike 2 → 1 and 3 → 1 melting, the disproportion 2 → 3 transition is a slightly cooperative one and observed over a wide temperature range. At [Me 2+ ] ∼ 10 −3 M , the temperature interval of A2U stability is not less than 20°C. In the case of Cd 2+ , it increases with the rise of ion concentration due to the decrease of T m 2→3 . The T m 3→1value is practically unchanged up to [Cd 2+ ] ∼10 −3 M . Differences between diagrams for Mg 2+ and Cd 2+ result from the various kinds of ion binding to poly(rA) · poly‐(rU) and poly(rA). © 2005 Wiley Periodicals, Inc. Biopolymers 78: 275–286, 2005