Rahman A, Hadi S M, Parish J H, Ainley K
Department of Biochemistry, Faculty of Life Sciences, Aligarh Muslim University, India.
Carcinogenesis. 1989 Oct;10(10):1833-9. doi: 10.1093/carcin/10.10.1833.
The naturally occurring flavonoid, quercetin, in the presence of Cu(II) and molecular oxygen caused breakage of calf thymus DNA, supercoiled pBR322 plasmid DNA and single-stranded M13 phage DNA. In the case of the plasmid, the product(s) were relaxed circles or a mixture of these and linear molecules depending upon the conditions. For the breakage reaction, Cu(II) could be replaced by Fe(III) but not by other ions tested [Fe(II), Co(II), Ni(II) and Ca(II)]. Structurally related flavonoids, rutin, galangin, apigenin and fisetin, were ineffective or less effective than quercetin in causing DNA breakage. In the case of the quercetin--Cu(II) reaction, Cu(I) was shown to be an essential intermediate by using the Cu(I)-sequestering reagents, neocuproine and bathocuproine. By using Job plots we established that, in the absence of DNA, five Cu(II) ions can be reduced by one quercetin molecule; in contrast, two ions were reduced per quercetin molecule in the DNA breakage reaction. Equally neocuproine inhibited the DNA breakage reaction. The involvement of active oxygen in the reaction was established by the inhibition of DNA breakage by superoxide dismutase, iodide, mannitol, formate and catalase (the inhibition was complete in the last case). From these data we propose a mechanism for the DNA strand scission reaction of quercetin and related flavonoids.
天然存在的类黄酮槲皮素在铜（II）和分子氧存在的情况下，会导致小牛胸腺DNA、超螺旋pBR322质粒DNA和单链M13噬菌体DNA断裂。对于质粒而言，根据条件不同，产物为松弛环或这些与线性分子的混合物。对于断裂反应，铜（II）可被铁（III）替代，但不能被其他测试离子[铁（II）、钴（II）、镍（II）和钙（II）]替代。结构相关的类黄酮芦丁、高良姜素、芹菜素和漆黄素在导致DNA断裂方面无效或比槲皮素效果差。在槲皮素 - 铜（II）反应中，通过使用铜（I）螯合剂新亚铜试剂和2,9 - 二甲基菲咯啉，表明铜（I）是必需的中间体。通过绘制乔布曲线我们确定，在没有DNA的情况下，一个槲皮素分子可以还原五个铜（II）离子；相反，在DNA断裂反应中每个槲皮素分子还原两个离子。同样，新亚铜试剂抑制DNA断裂反应。超氧化物歧化酶、碘化物、甘露醇、甲酸盐和过氧化氢酶对DNA断裂的抑制作用（最后一种情况下抑制作用完全）证明了活性氧参与该反应。根据这些数据，我们提出了槲皮素及相关类黄酮的DNA链断裂反应机制。
