The Formation of DNA Sugar Radicals from Photoexcitation of Guanine Cation Radicals

In this investigation of radical formation and reaction in gamma - irradiated DNA and model compounds, we report the conversion of the guanine cation radical (one-electron oxidized guanine, G.+) to the C1' sugar radical and another sugar radical at the C3' or C4' position (designated...

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Bibliographic Details
Published in:Radiation research 2004-05, Vol.161 (5), p.582-590
Main Authors: Shukla, LI, Pazdro, R, Huang, J, DeVreugd, C, Becker, D, Sevilla, MD
Format: Article
Language:English
Subjects:
Salmonidae
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Summary:In this investigation of radical formation and reaction in gamma - irradiated DNA and model compounds, we report the conversion of the guanine cation radical (one-electron oxidized guanine, G.+) to the C1' sugar radical and another sugar radical at the C3' or C4' position (designated C3'./C4'.) by visible and UV photolysis. Electron spin resonance (ESR) spectroscopic investigations were performed on salmon testes DNA as well as 5'-dGMP, 3'-dGMP, 2'-deoxyguanosine and other nucleosides/nucleotides as model systems. DNA samples (25- 150 mg/ml D2O) were prepared with Tl3+ or Fe(CN)3-6 as electron scavengers. Upon gamma irradiation of such samples at 77 K, the electron-gain path in the DNA is strongly suppressed and predominantly G.+ is found; after UV or visible photolysis, the fraction of the C1' sugar radical increases with a concomitant reduction in the fraction of G.+. In model systems, 3'- dGMP+.; and 5'-dGMP+. were produced by attack of Cl.-2 on the parent nucleotide in 7 M LiCl glass. Subsequent visible photolysis of the 3'-dGMP+. (77 K) results predominantly in formation of C1'. whereas photolysis of 5'-dGMP+. results predominantly in formation of C3'./C4'.. We propose that sugar radical formation is a result of delocalization of the hole in the electronically excited base cation radical into the sugar ring, followed by deprotonation at specific sites on the sugar.
ISSN:0033-7587
DOI:10.1043/0033-7587(2004)161<0582:TFODSR>2.0.CO;2