Lesnik E A, Agranovich I M, Maslova R N, Varshavskiĭ Ia M
Mol Biol (Mosk). 1987 Sep-Oct;21(5):1352-9.
The rate constants of 1H----3H exchange between water and C8H-groups of purine residues of alternating polynucleotides: poly[d(A-C)].poly[d(G-T)] and poly[d(A-T)].poly[d(A-T)], as well as Escherichia coli DNA, dAMP and dGMP, in solutions with high concentration (4.3 or 6 M) CsF, in water ethanol (60%) solution and (in comparison) in 0.15 M NaCl were determined at 25 degrees C. The 1H----3H exchange rate exchange rate constants for adenylic (kA) and guanylic (kG) residues of polynucleotides were compared with the corresponding constant for DNA and mononucleotides. It was shown that at conditions when poly[d(G-T)] and poly[d(A-T)].poly[d(A-T)] exhibit the "X-form" CD spectrum, alteration of exchange rates in polynucleotides (approximately 2-fold increase in kA in CSF and approximately 1.5-fold decrease in kA and kG in 60% ethanol with 0.15 M NaCl) is due to the effect of solvents on the chemical reactivity of purine residues, but does not reflect a conformational transition. The analysis of these results allows us to conclude, that alternating polynucleotides under the above mentioned conditions retain roughly the conformations inherent in them in 0.15 M NaCl: poly[d(A-C)].poly[d(G-T)] conformation in 4.3 m CsF or 60% ethanol differs only insignificantly from the "canonic" B-DNA, whereas the poly[d(A-T)].poly[d(A-T)] conformation in 6 M CSF corresponds to B-alternating DNA.
在25℃下，测定了交替多核苷酸：聚[d(A-C)]·聚[d(G-T)]和聚[d(A-T)]·聚[d(A-T)]，以及大肠杆菌DNA、dAMP和dGMP中嘌呤残基的C8H基团与水之间的1H----3H交换速率常数，测定条件为高浓度（4.3或6M）CsF溶液、水乙醇（60%）溶液，并（作为对照）在0.15M NaCl溶液中。将多核苷酸中腺苷酸（kA）和鸟苷酸（kG）残基的1H----3H交换速率常数与DNA和单核苷酸的相应常数进行了比较。结果表明，当聚[d(G-T)]和聚[d(A-T)]·聚[d(A-T)]呈现“X型”圆二色光谱时，多核苷酸中交换速率的改变（在CsF中kA约增加2倍，在含0.15M NaCl的60%乙醇中kA和kG约降低1.5倍）是由于溶剂对嘌呤残基化学反应性的影响，而不反映构象转变。对这些结果的分析使我们能够得出结论，上述条件下的交替多核苷酸大致保留了它们在0.15M NaCl中固有的构象：4.3m CsF或60%乙醇中的聚[d(A-C)]·聚[d(G-T)]构象与“经典”B-DNA仅略有不同，而6M CsF中的聚[d(A-T)]·聚[d(A-T)]构象对应于B型交替DNA。
