Ito K, Kawanishi S
Department of Public Health, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Biochemistry. 1997 Feb 18;36(7):1774-81. doi: 10.1021/bi9620161.
Pterin-sensitized DNA photodamage has been characterized by a DNA sequencing technique. Exposure of double-stranded DNA to 365-nm light in the presence of pterin, 6-carboxypterin, biopterin, neopterin, and folic acid produced sequence-specific DNA lesions, whereas photoinduced DNA lesions were not observed in the presence of xanthopterin or isoxanthopterin. The DNA photodamage induced by these pterin derivatives occurred specifically at the guanine located 5' to guanine. High-pressure liquid chromatography (HPLC) analysis revealed that the pterin-sensitized DNA photodamage was predominantly due to the formation of 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-oxo-dG). The DNA photodamage with pterin was not enhanced in D2O, suggesting that lO2 is not the main active species. Electron spin resonance (ESR) spin destruction experiments demonstrated that the photoexcited pterins reacted specifically with dGMP to produce pterin anion radicals. In addition, the reactivities of the photoexcited pterin derivatives with dGMP were found to correlate well with their efficiencies of DNA photodamage induction. These results indicate that the photoexcited pterins specifically oxidize deoxyguanosine in DNA to produce 8-oxo-dG through an electron transfer reaction. With denatured single-stranded DNA, the extent of pterin-sensitized photodamage was decreased and the damage occurred at most guanine residues without specificity for those located 5' to guanine. The mechanism of pterin-induced sequence-specific guanine photodamage could be explained on the basis of a recent theoretical study [Sugiyama. H., & Saito, I. (1996) J. Am. Chem. Soc. 118, 7063-7068] concerning the ionization potentials of stacked dinucleotide base pairs. Sepiapterin, a model compound for the dihydropterins, induced similar sequence-specific photolesions in double-stranded DNA. However, DNA photodamage by sepiapterin was more extensive in the presence of Cu(II), and the sites of the photolesions were different from those induced in the absence of Cu(II). These data may provide a basis for the elucidation of the molecular mechanism of solar UV carcinogenesis.
蝶呤敏化的DNA光损伤已通过一种DNA测序技术进行了表征。在蝶呤、6-羧基蝶呤、生物蝶呤、新蝶呤和叶酸存在的情况下，将双链DNA暴露于365纳米的光下会产生序列特异性的DNA损伤，而在黄蝶呤或异黄蝶呤存在的情况下未观察到光诱导的DNA损伤。这些蝶呤衍生物诱导的DNA光损伤特别发生在鸟嘌呤5'端的鸟嘌呤处。高压液相色谱（HPLC）分析表明，蝶呤敏化的DNA光损伤主要是由于7,8-二氢-8-氧代-2'-脱氧鸟苷（8-氧代-dG）的形成。在重水中，蝶呤引起的DNA光损伤并未增强，这表明单线态氧不是主要的活性物种。电子自旋共振（ESR）自旋破坏实验表明，光激发的蝶呤与dGMP特异性反应生成蝶呤阴离子自由基。此外，发现光激发的蝶呤衍生物与dGMP的反应活性与其诱导DNA光损伤的效率密切相关。这些结果表明，光激发的蝶呤通过电子转移反应特异性地氧化DNA中的脱氧鸟苷以产生8-氧代-dG。对于变性的单链DNA，蝶呤敏化的光损伤程度降低，损伤发生在大多数鸟嘌呤残基处，对位于鸟嘌呤5'端的那些残基没有特异性。基于最近关于堆积二核苷酸碱基对电离势的理论研究[Sugiyama. H., & Saito, I. (1996) J. Am. Chem. Soc. 118, 7063 - 7068]，可以解释蝶呤诱导的序列特异性鸟嘌呤光损伤的机制。二氢蝶呤的模型化合物sepiapterin在双链DNA中诱导了类似的序列特异性光损伤。然而，在Cu(II)存在的情况下，sepiapterin引起的DNA光损伤更广泛，并且光损伤的位点与在没有Cu(II)的情况下诱导的位点不同。这些数据可能为阐明太阳紫外线致癌作用的分子机制提供基础。
