McConnell B
Department of Biochemistry and Biophysics, John A. Burns School of Medicine, University of Hawaii, Honolulu 96822.
J Biomol Struct Dyn. 1984 Jun;1(6):1407-21. doi: 10.1080/07391102.1984.10507528.
An examination of the 1H NMR assignments and exchange properties of the amino resonances of the self-complementary tetramer, d(CGCG) was undertaken with regard to buffer effects, transfer of saturation from the water resonance and temperature dependence of amino 1H line shape and chemical shift. The lack of buffer effect on visible exchangeable proton resonances is evidence for the stringent requirement for nucleo-base protonation at pH values below neutrality, which is greatly reduced in the helical state. For this reason, sharp resonances are observed for both Watson-Crick and non-Watson-Crick cytosine amino protons for base-paired regions. Considerations of monomeric exchange mechanisms for the cytosine and guanine amino protons formed the basis for successful assignment and isolation of their resonances in the helical state by presaturation of the water resonance at selected pH values. Preirradiation of the water resonance at pH less than 6 would isolate the guanine amino 1H resonances of any self-complementary oligonucleotide, to exploit its high sensitivity as a useful proble of helix in equilibrium coil premelting.
针对缓冲液效应、水共振饱和转移以及氨基¹H线形状和化学位移的温度依赖性，对自互补四聚体d(CGCG)的氨基共振的¹H NMR归属和交换特性进行了研究。在低于中性的pH值下，对可见可交换质子共振缺乏缓冲液效应，这证明了核碱基质子化的严格要求，而在螺旋状态下这种要求大大降低。因此，对于碱基配对区域的沃森-克里克和非沃森-克里克胞嘧啶氨基质子都观察到了尖锐的共振。对胞嘧啶和鸟嘌呤氨基质子的单体交换机制的考虑，构成了通过在选定pH值下预饱和水共振成功归属和分离其在螺旋状态下的共振的基础。在pH小于6时对水共振进行预辐照，将分离出任何自互补寡核苷酸的鸟嘌呤氨基¹H共振，以利用其作为螺旋处于平衡态-线圈预熔状态下的有用探针的高灵敏度。
