Oxidative modification of guanine bases initiated by oxyl radicals derived from photolysis of azo compounds.
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 (O(2)(*-)) 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 O(2)(*-) 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 O(2)(*-) 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.
Shao
Jie
J
Chemistry Department, 31 Washington Place, New York University, New York, New York 10003-5180, USA.
Geacintov
Nicholas E
NE
Shafirovich
Vladimir
V
D000578:Amidines / Q000737:chemistry; D001391:Azo Compounds / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry*; D007700:Kinetics; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010782:Photolysis; D013481:Superoxides / Q000737:chemistry* / Q000378:metabolism
D000578:Amidines; D001391:Azo Compounds; D013481:Superoxides; D006147:Guanine; C046728:2,2'-azobis(2-amidinopropane)