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A Calorimetric Investigation of the Heats of Binding of Mg ++ to Poly A, to Poly U, and to Their Complexes
Author(s) -
Krakauer H.
Publication year - 1972
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.1972.360110406
Subject(s) - chemistry , stacking , mole , ion , solvent , base (topology) , binding energy , crystallography , organic chemistry , physics , mathematical analysis , mathematics , nuclear physics
The heats of binding of Mg ++ ions to poly A, poly U, and to their complexes, in the presence of Na + ions, have been measurd calorimetrically. In all cases the heat, ΔH(θ), exhibitis a distinct dependence on the extent of binding, θ, and in the cases of poly A and poly U also on the Na + concentration. The values of ΔH(θ) range from +2 to +3 kcal/mole of Mg ++ bound at θ = 0 to 1.3 kcal/mole at θ = 0.5 except in poly A where at θ = 0 ΔH(θ) = −2 to −3 kcal/mole. This is interpreted as being due to a facilitation of base stacking by the binding of Mg ++ . The extent of facilitation is consistent with current estimates of base stacking. A similar effect but of much smaller magnitude is believed to obtain in poly A poly U. An interpretation of the dependence of ΔH(θ) on θ in terms of simple electrostatic interactions, but neglecting solvent effects, was attempted and found to be inadequate.