A proton NMR spin-lattice relaxation study of the imino proton exchange kinetics in calf-thymus DNA
✍ Scribed by Peter Bendel
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1987
- Tongue
- English
- Weight
- 794 KB
- Volume
- 26
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Synopsis
The results of semiselective 'H-nmr inversion recovery experiments on mnicated calf thymus DNA fragments are reported. The measurements were conducted in aqueous solutions containing 85% D20, in order to reduce the dipolar contribution to the observed relaxation rates. In solutions containing 0.2M NaC1, 0.4 mM EDTA, and 10 mM cacodylate at pH = 7.0, the exchange rates of the imino protons in A-T base pairs c o n h values published earlier in the literature, extrapolating to 0.25 s-' 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 25OC), 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(r1)-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 X lo3 s-' for the A-T, and 50 s-' for the G-C, base paris at 62OC.