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(Yermilov et al., 1995), and this may most likely be due to its rapid degradation
by peroxynitrite (Uppu et al. 1996). 8-Nitroguanine is a typical peroxynitrite-
induced product, but to become prominent CO
2
has to be present (Yermilov et
al. 1996). On the other hand, CO
2
inhibits SSB formation by suppressing the
•
OH
route in peroxynitrite decomposition (Chap.2.2). The 8-nitroguanine lesion is
sensitive to hydrolysis, and, in phosphate buffer at 37 °C, it is eliminated from
DNA within a couple of hours (Yermilov et al. 1995; for a review on the biological
effects peroxynitrite-induced DNA damage see Szabo and Ohshima 1997).
When methyl radicals (formed in the reaction of Fe
2+
/EDTA/H
2
O
2
in the
presence of DMSO; Chaps 2.5 and 3.2) were reacted with RNA, considerable
methylation at the purines was observed (formation of 8MeGua, 2MeAde and
8MeAde; Kang et al. 1993). Surprisingly, the 2-methyladenine/8-methyladenine
ratio strongly falls upon increasing the pH from 5.2 to 9.2.
Peroxyl radicals, generated in the photolysis of aerated solutions of adequate-
ly functionalized acetophenones, oxidize selectively the G a high preference in
the formation of 8-oxo-G as compared to Z/Iz (Adam et al. 2001b). Whereas 8-
oxo-G (in experiments with dGuo) is further oxidized to 4-HO-8-oxo-G by per-
oxyl radicals (Chap. 10.13), the 8-oxo-G lesion within DNA seems to be much
more stable against peroxyl radical attack (Adam et al. 2001a). The 8-oxo-G le-
sion can serve as a sink for oxidative damage in DNA (Sect. 12.10.3). The radical
that is formed reacts readily with O
2
•
−
(ssDNA: 1.3
10
8
dm
3
mol
−1
s
−1
; dsDNA:
×
10
9
dm
3
mol
−1
s
−1
), leading mainly to dehydroguanodinohydantoin lesions
(Misiaszek et al. 2005).
1.0
×
12 . 4
Sugar Damage
12 . 4.1
General Remarks
When the sugar moiety is damaged, important lesions such as abasic sites and
strand breaks are induced. In the course of these reactions, unaltered bases are
released. This may be considered as a loss of information, but the situation seems
to be much more complex than that (Kroeger et al. 2004a). Some aspects of
•
OH
attack on the sugar moiety in competition to attack at the bases have already
been dealt with above. Here, the products and the reactions that are leading to
these products will be discussed. In poly(U) and poly(C) damage amplification
reactions involving the sugar moiety do occur (Chap. 11.2; for corresponding re-
actions in other polymers see Chap. 9.4). On the dinucleotide level such reactions
are also observed (Chap. 10.3), but for DNA strong evidence is still missing.
12 . 4. 2
Abasic Sites
As the word suggests, an abasic site (apurinic/apyrimidinic site, AP) lacks the base,
but the DNA backbone is more or less intact. The simplest AP is a 2-dR site, formed
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