Oxidative Modification of Guanine Bases Initiated by Oxyl Radicals Derived from Photolysis of Azo Compounds

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• 作者：Jie Shao ; Nicholas E. Geacintov ; Vladimir Shafirovich
• 刊名：Journal of Physical Chemistry B
• 出版年：2010
• 出版时间：May 20, 2010
• 年：2010
• 卷：114
• 期：19
• 页码：6685-6692
• 全文大小：254K
• 年卷期：v.114,no.19(May 20, 2010)
• ISSN：1520-5207

文摘

Oxidative damage to guanine bases initiated by photolysis of the water-soluble radical generator 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) has been investigated by laser kinetic spectroscopy. In the neutral oxygenated aqueous solutions, 355 nm laser flash photolysis of AAPH generates a whole spectrum of free radicals including 2-amidinoprop-2-peroxyl (ROO^•), 2-amidinoprop-2-oxyl (RO^•), and superoxide (O₂^•−) radicals. These oxyl radicals with negligible absorption in a near UV−visible range were monitored in the reactions leading to the products with characteristic absorption spectra. This approach reveals that RO^• radicals induce fast one-electron oxidation of 2′-deoxyguanosine (dG) to form guanine neutral radicals, dG(−H)^•. In contrast, ROO^• radicals do not react at observable rates with dG. The O₂^•− radicals were detected using a classical test reaction with tetranitromethane to form nitroform. The major pathway for formation of the end-products of guanine oxidation is the combination of the G(−H)^• and O₂^•− radicals to form 2,5-diamino-4H-imidazolone (Iz). This mechanism was confirmed by analysis of the end-products produced by oxidation of two substrates: (1) the guanosine derivative 2′,3′,5′-tri-O-acetylguanosine (tri-O-Ac-G) and (2) the 5′-d(CCATCGCTACC) sequence. The major products isolated by HPLC and identified by mass spectrometry methods were the tri-O-Ac-Iz and 5′-d(CCATC[Iz]CTACC products.