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Interaction of poly(X) with poly(U): Alkali metal ion specificity suggests a four‐stranded helix
Author(s) -
Roy Kunal B.,
Frazier J.,
Miles H. Todd
Publication year - 1983
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.360220903
Subject(s) - chemistry , alkali metal , helix (gastropod) , crystallography , metal , ion , infrared spectroscopy , ionization , metal ions in aqueous solution , organic chemistry , ecology , snail , biology
Interaction of poly(X) with poly(U) to form a regular, ordered structure has been investigated by uv, CD, and ir spectroscopy. The XU complex exhibits a marked dependence of T m on the nature of the alkali metal ion present in solution. Stability of the complex is surprisingly high and increases with ionization of X residues at N3. The ir evidence shows the U residues are present as the diketo form and X residues as the 6‐keto‐2‐enolate anion and indicates that the X and U carbonyl groups are vibrationally coupled. A mixing curve exhibits a single minimum, at 1:1, but we conclude that the actual combining ratio is twice this value and that the formula of the complex is X 2 U 2 . We propose a model based on a four‐standard helix with size‐specific alkali metal complexing to X and U carbonyl oxygens in the axial channel of the helix. This model and previously suggested two‐stranded structures are evaluated in terms of the physical and chemical properties of the complex.