Abstract
Guanine is the most easily oxidized among the four DNA bases, and some guanine-rich sequences can form quadruplex structures. In a previous study using 6-mer DNA d(TGGGGT), which is the shortest oligomer capable of forming quadruplex structures, we demonstrated that guanine oxidation products of quadruplex DNA differ from those of single-stranded DNA. Therefore, the hotooxidation products of double-stranded DNA (dsDNA) may also differ from that of quadruplex or single-stranded DNA, with the difference likely explaining the influence of DNA structures on guanine oxidation pathways. In this study, the guanine oxidation products of the dsDNA d(TGGGGT)/d(ACCCCA) were analyzed using HPLC and electrospray ionization-mass spectrometry (ESI-MS). As a result, the oxidation products in this dsDNA were identified as 2,5-diamino-4H-imidazol-4-one (Iz), 8-oxo-7,8-dihydroguanine (8oxoG), dehydroguanidinohydantoin (Ghox), and guanidinohydantoin (Gh). The major oxidation products in dsDNA were consistent with a combination of each major oxidation product observed in single-stranded and quadruplex DNA. We previously reported that the kinds of the oxidation products in single-stranded or quadruplex DNA depend on the ease of deprotonation of the guanine radical cation (G•+) at the N1 proton. Similarly, this mechanism was also involved in dsDNA. Deprotonation in dsDNA is easier than in quadruplex DNA and more difficult in single-stranded DNA, which can explain the formation of the four oxidation products in dsDNA.
Highlights
Environmental agents, such as UV-light or free radicals, often oxidize DNA bases and oxidation of DNA bases is accepted as one of the principal sources of genetic damage involved in genetic mutation, aging, and cell death [1,2,3,4,5,6,7,8]
Since an increase in the circular dichroism (CD) spectrum around 250–300 nm, which is typical of B-form double-stranded DNA (dsDNA), was detected in
In a previous report [17], the oxidation products in single-stranded or quadruplex DNA were found to depend on the ease of deprotonation at the N1 proton of G+
Summary
Environmental agents, such as UV-light or free radicals, often oxidize DNA bases and oxidation of DNA bases is accepted as one of the principal sources of genetic damage involved in genetic mutation, aging, and cell death [1,2,3,4,5,6,7,8]. The oxidation products of quadruplex DNA were compared with that of single-stranded DNA in a study using 6-mer DNA d(TGGGGT), which is the shortest oligomer among the quadruplex-forming sequences in the presence of several ions [16]. The discussion that DNA structure influences the types of photooxidation products is important, and similar discussions have been reported [18,19]. The types of guanine oxidation products depend on the structure of quadruplex or single-stranded. May differ from that of quadruplex or single-stranded DNA, and that the differences in these guanine oxidation products are likely to explain the influence of DNA structures on guanine oxidation pathways. To fully understand differences in guanine oxidation pathways in single-stranded, double-stranded and quadruplex DNA, we attempted a direct, simultaneous analysis of the types, yields, and sites of. Using d(TGGGGT) [17], the oxidation products in dsDNA were compared with the products in single-stranded or quadruplex DNA
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