Reductive damage in directly ionized DNA: saturation of the C5=C6 bond of cytosine in d(CGCG)(2) crystals.
Electron paramagnetic resonance (EPR) was used to study an oligodeoxynucleotide duplex of d(CGCG)(2) that is known to crystallize in Z-form. After X irradiation at 4 K, EPR data were collected on single crystals and polycrystalline samples as a function of annealing temperature and dose. A radical produced by the net gain of a hydrogen atom at C6 and a proton at N3, Cyt(C6+H, N3+H(+))(+*), is identified. This radical had not been positively identified in polymeric DNA previously. The Cyt(C6+H, N3+H(+))(+*) makes up about 4% of the total radical population at 4 K, increasing to about 10-15% after the DNA is annealed to 240 K. There appears to be neither an increase nor a decrease in the absolute concentration of Cyt(C6+H, N3+H(+))(+*) upon annealing from 4 K to 240 K. Additionally, the presence of another radical, one due to the net gain of hydrogen at C5 of cytosine, the Cyt(C5+H)(*), is implicated. Together, these two radicals appear to account for 60-80% of the reduced species in DNA that has been irradiated at 4 K and annealed to 240 K.
Debije
Michael G
MG
Department of Biochemistry and Biophysics, University of Rochester, Rochester, New York 14642, USA.
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David M
DM
Bernhard
William A
WA
D002244:Carbon / Q000737:chemistry*; D003596:Cytosine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry / Q000528:radiation effects*; D004578:Electron Spin Resonance Spectroscopy; D010084:Oxidation-Reduction; D014965:X-Rays
D002244:Carbon; D003596:Cytosine; D004247:DNA