Howard F B, Miles H T
Biochemistry. 1984 Dec 18;23(26):6723-32. doi: 10.1021/bi00321a068.
Polynucleotide helices formed by the interaction of (d2NH2A)n, (r2NH2A)n, (dT)n, and (rT)n have been prepared and their physical and spectroscopic properties examined. Thermal transitions, dependence of Tm on salt concentration, stoichiometry, phase diagrams, and calculated enthalpies are reported. UV, CD, and IR spectra are reported. All of the deoxy-deoxy helices containing 2NH2A have positive CD first extrema near 290 nm and appear to have B-form structure. All the ribo-ribo or hybrid helices have negative first extrema in this region and appear to have A-form structure. Elevation of Tm by the 2-NH2 group of 2NH2A is much smaller in the deoxy than in the ribo series. We have applied an equation based on the electrostatic theory of Manning [Manning, G.S. (1972) Bopolymers 11, 937-949; Manning, G.S. (1978) Q. Rev. Biophys. 11, 179-246; Record M.T., Anderson, C.F., & Lohman, T.M. (1978) Q. Rev. Biophys. 11, 103-178] to calculate ethalpies of the helix-coil transitions of the complexes reported here. These calculated enthalpies are larger for 2NH2A X T than for A X T helices, but the difference is much smaller in the deoxy than in the ribo series. We attribute these effects on Tm and delta H in the deoxy series to loss of stabilization of the spine of hydration in B-form structures caused by interference of the 2-NH2 group in the minor groove of the helix [Dickerson, R.E., Drew, H.R., Conner, B.N., Wing, R.M., Fratini, A.V., & Kopka, M.L. (1982) Science (Washington, D.C.) 216, 475-485]. Complete phase diagrams for all 2NH2A,T systems and some A,T systems are reported. The diagrams differ widely and can be placed in four groups according to the number of transitions each system possesses.
已制备出由(d2NH2A)n、(r2NH2A)n、(dT)n和(rT)n相互作用形成的多核苷酸螺旋，并对其物理和光谱性质进行了研究。报告了热转变、熔点（Tm）对盐浓度的依赖性、化学计量比、相图以及计算出的焓。还报告了紫外、圆二色（CD）和红外光谱。所有含2NH2A的脱氧-脱氧螺旋在290nm附近的CD第一个极值为正，似乎具有B型结构。所有核糖-核糖或杂交螺旋在该区域的第一个极值为负，似乎具有A型结构。在脱氧系列中，2NH2A的2-NH2基团对Tm的升高作用比核糖系列小得多。我们应用了一个基于曼宁静电理论的方程[曼宁，G.S.（1972年）《高分子聚合物》11，937 - 949；曼宁，G.S.（1978年）《生物物理学季评》11，179 - 246；里德，M.T.，安德森，C.F.，& 洛曼，T.M.（1978年）《生物物理学季评》11，103 - 178]来计算此处报道的复合物螺旋-线圈转变的焓。对于2NH2A×T螺旋，这些计算出的焓比A×T螺旋的大，但在脱氧系列中的差异比核糖系列小得多。我们将脱氧系列中对Tm和ΔH的这些影响归因于螺旋小沟中2-NH2基团的干扰导致B型结构中水分子骨架稳定性的丧失[迪克森，R.E.，德鲁，H.R.，康纳，B.N.，温，R.M.，弗拉蒂尼，A.V.，& 科普卡，M.L.（1982年）《科学（华盛顿特区）》216，475 - 485]。报告了所有2NH2A，T系统和一些A，T系统的完整相图。这些相图差异很大，可根据每个系统所具有的转变数量分为四类。
