DNA and Double-Stranded Oligonucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 380

10 −7 mol J −1 , respectively (Bourdat et al. 2000; Cadet et yields, 0.001 and 0.013 ×

al. 2002).

10 −7 mol J −1 . Thus
the tandem lesions contribute about 10% of the total 8-oxo-G yield in DNA.
Using another approach to isolate these lesions gave G (Fo/8-oxo-G) = 0.12

Under the same conditions, the total 8-oxo-G yield is 0.13 ×

×

10 −7 mol J −1 , i.e. a value which is an order of magnitude higher (Maccubbin et
al. 2000). In this study, this lesion was also observed in the absence of O 2 , albeit
with a much lower yield. Since Fo can only be formed in the presence of O 2 ,
one must conclude that these samples were not fully deoxygenated. When the
effect of EDTA-Fe 2+ was studied, it was observed that the yield of these lesions
increased with time (Bourdat et al. 2000). It was not realized that EDTA-Fe 2+
readily autoxidizes in the presence of O 2 and that this reaction is connected with
a concomitant formation of • OH (Yurkova et al. 1999; Chap. 2.5). Mechanistic
details seem now to be reasonably well established and have been discussed in
Chapter 10.6. The mechanism originally suggested (Bourdat et al. 2000), name-
ly that the T-derived peroxyl radical oxidizes a neighboring G by one-electron
oxidation, is very unlikely considering that the reduction potential of this kind
of peroxyl radicals is only +0.8 V (Chap. 8.3) and the reduction potential of G
is near +1.3 V (see above) rendering this reaction markedly endothermic. This
point has been raised here, since oxidation of G observed in systems that involve
peroxyl radicals sometimes make use of the ET concept.
The action of nuclease P1 on the 8-oxo-G/Fo lesion has been studied on the
model level (Maccubin et al. 1992).
In the absence of O 2 , the G^T lesion is formed in DNA that has been -irradi-

ated in aqueous solution (Box et al. 2000; for model systems see Chap. 10.5).

γ