A Calorimetric Investigation of the Heats of Binding of Mg++ to Poly A, to Poly U, and to Their Complexes

✍ Scribed by H. Krakauer

• Publisher: Wiley (John Wiley & Sons)
• Year: 1972
• Tongue: English
• Weight: 800 KB
• Volume: 11
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1972.360110406

✦ Synopsis

State Trniversity

Synopsis

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, AH(@), exhibitis a distinct dependence on the extent of binding, 8, and in the cases of poly A and poly U also on the Na+ concentration. The values of A H ( 0 ) range from + 2 to +3 kcal/ mole of Mg++ bound at 0 = 0 to 1.3 kcal/mole a t 0 = 0.5 except in poly A where a t e = 0 AH(@) = -2 to -3 kcal/mole. This is interpreted as being due to a facilitation of base stacking by the binding of hag++. 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 AH(@) on 0 in terms of simple electrostatic interactions, but neglecting solvent effects, was attempt,ed and found to be inadequate.