Maiti Motilal, Das Suman, Sen Anjana, Das Arunangshu, Kumar Gopinatha Suresh, Nandi Ruma
Biophysical Chemistry Laboratory, Indian Institute of Chemical Biology, 4 Raja S.C. Mullick Road, Kolkata 700032, India.
J Biomol Struct Dyn. 2002 Dec;20(3):455-64. doi: 10.1080/07391102.2002.10506864.
Sanguinarine exhibits pH dependent structural equilibrium between iminium form (structure I) and alkanolamine form (structure II) with a pKa of 7.4 as revealed from spectrophotometric titration. The titration data show that the compound exists almost exclusively as structure I and structure II in the pH range 1 to 6 and 8.5 to 11, respectively. The interaction of structure I and structure II to several B-form natural and synthetic double and single stranded DNAs has been studied by spectrophotometric, spectrofluorimetric and circular dichroic measurements in buffers of pH 5.2 and pH 10.4 where the physicochemical properties of DNA remain in B-form structure. The results show that structure I bind strongly to all B-form DNA structures showing typical hypochromism and bathochromism of the alkaloid's absorption maximum, quenching of steady-state fluorescence intensity and perturbations in circular dichroic spectrum. The structure II does not bind to DNA, but in presence of large amount of DNA significant population of structure I is generated, which binds to DNA and forms a structure I-DNA intercalated complex. The nature and magnitude of the spectral pattern are very much dependent on the structure as well as base composition of each DNA. The generation of the structure I from structure II is significantly affected by increasing ionic strength of the medium. The conversion of structure II to structure I in presence of high concentration of DNA in solution is explained through formation of a binding equilibrium process between structure II and structure I-DNA intercalated complex.
从分光光度滴定法可知，血根碱在亚胺离子形式（结构I）和链烷醇胺形式（结构II）之间呈现pH依赖性结构平衡，其pKa为7.4。滴定数据表明，该化合物在pH值1至6和8.5至11的范围内几乎分别仅以结构I和结构II存在。在pH 5.2和pH 10.4的缓冲液中，通过分光光度法、荧光光谱法和圆二色性测量研究了结构I和结构II与几种B型天然和合成双链及单链DNA的相互作用，在这些缓冲液中DNA的物理化学性质保持在B型结构。结果表明，结构I与所有B型DNA结构强烈结合，表现出生物碱最大吸收峰典型的减色和红移、稳态荧光强度猝灭以及圆二色光谱的扰动。结构II不与DNA结合，但在大量DNA存在的情况下会产生大量结构I，其与DNA结合并形成结构I-DNA插入复合物。光谱模式的性质和强度在很大程度上取决于每种DNA的结构以及碱基组成。介质离子强度的增加对结构II向结构I的转化有显著影响。通过结构II与结构I-DNA插入复合物之间形成结合平衡过程来解释在溶液中高浓度DNA存在下结构II向结构I的转化。
