Gorenstein D G, Lai K
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907.
Biochemistry. 1989 Apr 4;28(7):2804-12. doi: 10.1021/bi00433a010.
31P NMR provides a convenient monitor of the phosphate ester backbone conformational changes upon binding of the intercalating drugs ethidium, quinacrine, and daunomycin to sonicated poly(A).poly(U) and calf thymus DNA. 31P chemical shifts can also be used to assess differences in the duplex unwinding angles in the presence of the drug. Thus a new 31P signal, 1.8-2.2 ppm downfield from the double-stranded helix signals, is observed in the ethidium ion-poly(A).poly(U) complex. This signal arises from phosphates which are in perturbed environments due to intercalation of the drug. This is in keeping with the hypothesis that the P-O ester torsional angle in phosphates linking the intercalated base pairs is more trans-like. Similar though smaller deshielding of the 31P signals is observed in sonicated poly(A).poly(U)-quinacrine complexes as well as in the daunomycin complexes. The effect of added ethidium ion, quinacrine, and daunomycin on the 31P spectra of sonicated calf thymus DNA is consistent with Wilson and Jones' (1982) earlier study. In these drug-DNA complexes the drug produces a gradual downfield shift in the DNA 31P signal without the appearance of a separate downfield peak. These differences are attributed to differences in the rate of chemical exchange of the drug between free and bound duplex states. The previous correlation of 31P chemical shift with drug duplex unwinding angle (Wilson & Jones, 1982) is confirmed for both the RNA and DNA duplexes.
31P核磁共振提供了一种便捷的监测手段，可用于观察嵌入药物（如溴化乙锭、喹吖因和柔红霉素）与经超声处理的聚（A）·聚（U）及小牛胸腺DNA结合时，磷酸酯主链构象的变化。31P化学位移还可用于评估药物存在时双链解旋角度的差异。因此，在溴化乙锭离子-聚（A）·聚（U）复合物中观察到一个新的31P信号，相对于双链螺旋信号向低场位移1.8 - 2.2 ppm。该信号源自因药物嵌入而处于受扰环境中的磷酸盐。这与下述假设相符，即连接嵌入碱基对的磷酸盐中P - O酯扭转角更接近反式。在经超声处理的聚（A）·聚（U） - 喹吖因复合物以及柔红霉素复合物中也观察到了类似但较小的31P信号去屏蔽现象。添加溴化乙锭离子、喹吖因和柔红霉素对经超声处理的小牛胸腺DNA的31P谱的影响与威尔逊和琼斯（1982年）早期的研究结果一致。在这些药物 - DNA复合物中，药物使DNA的31P信号逐渐向低场位移，而未出现单独的低场峰。这些差异归因于药物在游离态和结合态双链之间化学交换速率的不同。对于RNA和DNA双链，均证实了先前31P化学位移与药物双链解旋角度之间的相关性（威尔逊和琼斯，1982年）。
