Chemistry Reference
In-Depth Information
Table 12.6.
γ
-Radiolysis of suspended mamalian chromation in aqueous solution under
different gassing conditions.
G
values in units of 10
−9
mol J
−1
Product
Ar
N
2
O
Air
N
2
O/O
2
n.d.
a
5,6H
2
T
0.48
0.26
n.d.
b
b
5OH5MeHyd
0.21
0.42
b
b
b
5OHHyd
0.22
Cg
0.5
0.95
1.1
2.3
5OH5,6H
2
T
0.3
0.3
n.d.
n.d.
5OH5,6H
2
Cy t
0.17
0.17
n.d.
n.d.
HmU
0.045
0.064
0.02
0.052
Tg
0.045
0.094
0.18
0.40
b
b
5OH6OHC
0.14
0.33
FAPY-A
0.82
0.96
0.60
1.02
8-oxo-A
0.45
0.80
1.10
3.50
FAPY- G
0.96
1.81
1.11
1.81
8-oxo-G
0.55
1.35
3.85
8.05
a
n.d., Not detected
b
No increase in the amount above the background level at doses up to 200 Gy
formation of these products has not yet been investigated. This effect has not
been observed in the case of chromatin irradiations (Table 12.6), and this must
be taken as a caveat not to overinterprete these data.
With chromatin suspensions, DNA product yields are an order of magnitude
lower as compared to DNA solutions. This is partially due to
•
OH-scavenging by
the nucleoproteins, but since one deals here with suspensions,
•
OH-scavenging
by dissolved impurities has an even more dramatic effect than in DNA solutions.
Moreover, some of the DNA damage may be repaired by the surrounding protein,
but the existing data do not provide a firm conclusion concerning this point.
The main detectable DNA lesions, as damaged bases are concerned, were also
found in irradiated cells. Table 12.7 compiles data that were obtained with
γ
(low
LET) and carbon ion (high LET) radiations.
As is seen from the table, the yield of detectable damaged bases is notice-
ably lower for the high LET radiation despite its higher RBE. This agrees with
the concept of clustered lesions being responsible for lethality (for the repair of
clustered lesions see Dianov et al. 2001).
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