【摘要】 在5mM浓度下,测定了NAD~+、εNAD~+、NMN~+、εAMP和(εAMP+RMN~+)混合物的化学位移与pH依赖关系。根据环流各向异性屏蔽效应,通过比较εNAD~+与等量混合物(εAMP+NMN~+)的对应碱基质子化学位移,以及比较εNAD~+与NAD~+的烟酰胺质子化学位移,发现在水溶液中的游离NAD~+以pK_a3.88为转折,处于不同构象:在pH3.88以下,NAD处于伸展构象;在此值以上,NAD~+处于折迭构象。更多还原

【Abstract】 pH dependence of the chemical shifts of NAD⁺, etheno-NAD⁺（εNAD）, NMN⁺,etheno-AMP （εAMP）and an equivalent mixture of ∈AMP and NMN⁺ have been inves-tigated by proton nuclear magnetic resonance at a concentration level of 0.005M. Inthe comparisons of the chemical shifts of corresponding protons of the bases betweenεNAD⁺ and NAD⁺ as well as between εNAD and the mixture of εAMP and NMN⁺ basedon ring current magnetic anisotropy, it is suggested that NAD⁺ in D₂O may exist intwo conformational forms with a pK_α of 3.88: it exists as an internally stacked format pH above 3.88 and in an open conformation at lower pK_α.更多还原