Chemistry Reference
In-Depth Information
Table 10. 33.
Photosensitization of dGuo by various sensitizers. Ratio of product distribu-
tion. (According to Ravanat et al. 1998)
Photosensitizer
(4-OH-8-oxo-G + 8-oxo-G)/Z
Zn-TRP
5.6
Methylene blue
3.6
TRP
2.3
Riboflavin
0.4
TRP = µ[meso-5,10,15,20-tetra(pyridyl)porphyrin]tetrakis[bis(bipyridine)chloride ruthenium(II)]
Table 10. 34.
Effect of photoexcited menadione, benzophenone and riboflavin on Thd,
dGuo and d(TpG). Degradation (+ = observed,
−
= not observed) and specific products in
the case of d(TpG). (Delatour et al. 1999)
Menadione
Benzophenone
Riboflavin
Thd
+
+
−
dGuo
−
+
+
d(TpG)
+
+
+
T
→
HMdU/FordU
+
+
−
dG
→
dZ
−
+
+
<d(TpG)>
+
+
−
product results from the O
2
(
1
g
) reaction (for the synthesis of oligonucleotides
that contain this lesion see Romieu et al. 1999d). The products are very sensi-
tive to further degradation, even at low conversions. In a mixture of dGuo and
8-oxo-G, the latter is practically fully degraded before dGuo starts to be con-
sumed (Ravanat et al. 2003). This has been attributed to the rapid oxidation of
8-oxo-G by G
•
(
k
= 4.6
∆
10
8
dm
3
mol
−1
s
−1
; Steenken et al. 2000). Moreover, the
×
reaction of O
2
(
1
∆
g
) with 8-oxo-G readily yields as the major product 1-(2-deoxy-
β
-D-erythro-pentofuranosyl)cyanuric acid (Raoul and Cadet 1996), but Z is also
among the products (Ravanat et al. 1998). In fact, methylene blue photooxidizes
8-oxo-G three times faster than dGuo (Buchko et al. 1995a). As a consequence,
the ratio of the product yields, shown for various sensitizers in Table 10.33, may
have a wide error bandwidth, but the data strongly indicate that sensitization by
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