Summerfield F W, Tappel A L
Biochim Biophys Acta. 1983 Jun 24;740(2):185-9. doi: 10.1016/0167-4781(83)90076-3.
DNA crosslinks made by malondialdehyde are fluorescent. The fluorescence is quenched by collision or intercalation. A 3.3-fold higher concentration of the external (collision) quencher KI was required to cause 50% quenching of the fluorescence of the interstrand-DNA crosslinks than to cause 50% quenching of the fluorescence of the model compounds Val2MDA and the malondialdehyde-crosslinked heterodimer of GMP and CMP. Thus, the crosslinked nucleotide dimers in the DNA were shown to be 70% shielded from the solvent. Similarly, DNA-protein crosslinks made by malondialdehyde were shown to be 55% shielded. The internal (intercalation) quencher Ag+ enhanced the fluorescence of the DNA crosslinks at concentrations below 0.3 mM; higher concentrations quenched the fluorescence. Concentrations of Ag+ below 10 mM did not affect the fluorescence of the model compounds. The calculated dissociation constant for Ag+ was much less at pH 5 than at pH 7 or 9. The observed binding of Ag+ and its pH dependence suggest that pi-stacking of adjacent bases strengthens the binding of Ag+ to the crosslinks. These results indicate that the crosslinks are in the interior of the DNA, so they may not easily be recognized by a repair system.
由丙二醛形成的DNA交联具有荧光性。荧光通过碰撞或嵌入作用而猝灭。相较于使模型化合物Val2MDA以及GMP和CMP的丙二醛交联异二聚体的荧光猝灭50%，使链间DNA交联的荧光猝灭50%需要浓度高3.3倍的外部（碰撞）猝灭剂KI。因此，DNA中的交联核苷酸二聚体有70%被溶剂屏蔽。同样，由丙二醛形成的DNA-蛋白质交联有55%被屏蔽。内部（嵌入）猝灭剂Ag⁺在浓度低于0.3 mM时增强DNA交联的荧光；更高浓度则使荧光猝灭。低于10 mM的Ag⁺浓度不影响模型化合物的荧光。计算得出的Ag⁺解离常数在pH 5时比在pH 7或9时小得多。观察到的Ag⁺结合及其pH依赖性表明相邻碱基的π-堆积增强了Ag⁺与交联的结合。这些结果表明交联位于DNA内部，因此它们可能不容易被修复系统识别。
