Nucleobases, Nucleosides and Nucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 226

Of these radicals, 60-70% have oxidizing properties (for the reactions of purine-
• OH-adducts with a number of reductants see, e.g., O'Neill 1983, 1984; O'Neill et
al. 1985; Shi et al. 1999a; Candeias and Steenken 2000). This includes the • OH-
adducts that eliminate rapidly water yielding G • (Steenken 1989). Its main pre-
cursor has been has been suggested to be the C (4)- • OH-adduct ( 60-70%; Vieira

et al. 1993; Candeias and Steenken 2000). This radical eliminates water leading
to the even more strongly oxidizing G • [cf. reaction (77)].
The C (8)- • OH-adduct has reducing properties, and from its rapid reaction
with Fe(CN) 6 3− or methylviologen its yield has been determined at 17% (Can-
deias and Steenken 2000). It is the precursor of FAPY-dGuo and 8-oxo-dGuo
whose combined yields have been determined after radiolysis in N 2 O-saturated
solutions at

∼

10% (Berger and Cadet 1985; lower limit for the C (8)- • OH-adduct).
The maximum yield of 8-oxo-dGuo in the presence of Fe(CN) 6 3− as oxidant and
in the acid pH range has been found to be 23% (von Sonntag and Schuchmann
2001). This must be taken as an upper limit, since under these conditions reac-
tion (51) may contribute to the formation of the C (8)- • OH-adduct.
The C (2)- • OH-adduct is likely to eliminate ammonia, and from the low am-
monia yield it seems not to exceed 1.5% (von Sonntag and Schuchmann 2001).
With dGuo, some H-abstraction occurs also at the sugar moiety. Among others,
this is indicated by an isomerization of dGuo (in low yields, see Table 10.13).
Nearly all sugar-derived radicals must have reducing properties, and, based on
the pulse radiolysis data mentioned above, the upper limit of their yield must be
much less than the total of 17%.
The reactions of • OH with dAdo/Ado are depicted in reactions (68)−(71).

∼