DNA and Double-Stranded Oligonucleotides - Free-Radical-Induced DNA Damage and Its Repair - page 371

Table 12.9. Kinetic isotope effects for the formation of some DNA products connected
with DNA strand breakage by • OH. (Balasubramanian et al. 1998)

Position deuterated 3 ′ -Phosphate 3 ′ -Phosphoglycolate 5 ′ -Aldehyde

5 ′ 1.67 ± 0.15 2.6 ± 0.5

4 ′ 1.09 ± 0.55 2.1 ± 0.3

3 ′ 1.14 ± 0.05

2 ′ 1.11 ± 0.02

1 ′ 1.08 ± 0.03

One of the most important sugar lesion is the 3 -phosphoglycolate that is typical-

ly formed in the presence of O 2 (for its excision by purified HeLa cell extracts see
Winters et al. 1992). Specifically deuterated nucleoside triphosphates were used
for incorporation into dsDNA by PCR (Balasubramanian et al. 1998). Hydroxyl
radicals were generated by a Fenton reaction, and the yields of free 3

′

′ -phosphate

end groups, 3 -aldehyde were measured. Depending on

the position of the deuteration, the yields vary with respect to a non-deuterated
sample (Table 12.9).
In the original paper (Balasubramanian et al. 1998), the observed marked iso-
tope effect has been connected with the accessibility of the various C

′ -phosphoglycolate and 5 ′

H groups, but
we note that in its H-abstraction reactions similarly high H/D-isotope effects are
observed for • OH (e.g., k (CH 3 OH)/ k (CD 3 OH) = 2.5, k (CH 3 CH 2 OH)/ k (CD 3 CD 2 OH)
= 1.6 and k ((CH 3 ) 2 CHOH)/ k ((CH 3 ) 2 CDOH) = 1.5; Anbar et al. 1966; more recently,
a value of 1.96 has been reported for the EtOH system; Bonifacic et al. 2003). For
the KIE to show up in an experiment, a competing reaction is required. Here, this
could be, for example, an addition of • OH to the nucleobases.
There is a general agreement that its formation of the 3

−

′ -phosphoglycolate

starts from the C (4 ′ ) radical [reactions (24)−(26)].