期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1979
卷号：76
期号：7
页码：3130-3134
DOI：10.1073/pnas.76.7.3130
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Real-time solvent exchange measurements using Fourier transform NMR at 270 MHz are presented. By means of the fast gel filtration column techniques originally developed for tritium exchange experiments, we were able to replace the solvent of a tRNA sample from an 1H2O to an 2H2O buffer and obtain a useful spectrum in 2-5 min. At 15 degrees C, there are 5 +/- 1 lowfield (-11 to -15 ppm relative to 2,2-dimethyl-2-silapentane-5-sulfonate) imino protons with exchange half times of minutes to hours. In addition, the m7G-46 C(8) proton and several amino protons are observed to exchange with similar rates. Analogous studies on unfractionated yeast tRNA suggest that such a class of slowly exchanging imino protons is present in several tRNAs, and that the activation energy for exchange is small [[approximatley 5 kcal/mol (21 kJ/mol)]. We speculate that these imino resonances arise from D-stem protons and that their slow exchange reflects stabilization by the numerous tertiary interactions involving this stem and the Mg2+ bound at the P-10 bend.
