ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The results of semiselective 1H-nmr inversion recovery experiments on sonicated calf thymus DNA fragments are reported. The measurements were conducted in aqueous solutions containing 85% D2O, in order to reduce the dipolar contribution to the observed relaxation rates. In solutions containing 0.2M NaCl, 0.4 mM EDTA, and 10 mM cacodylate at pH = 7.0, the exchange rates of the imino protons in A-T base pairs confirm values published earlier in the literature, extrapolating to 0.25 s-1 at 25°C. Corresponding values for the G-C base pairs are published for the first time, and are about sixfold slower. The addition of up to 0.1M Tris buffer (pH = 7.3 at 25°C), caused a striking increase in the measured exchange rates for both the A-T and G-C imino protons, resembling the effect recently observed for poly(rA)-poly(rU) and poly(rI)-poly(rC), and suggesting that the exchange rates measured for nucleic acid duplexes in low buffer concentrations at neutral pH do not reflect base-pair opening rates as assumed in the past. Lower limits to the base-pair opening rates could be estimated from extrapolation of the experimental data to infinite buffer concentration, and are 1 × 103 s-1 for the A-T, and 50 s-1 for the G-C, base paris at 62°C.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360260410
