Chemical and Biochemical Studies on Pathological Aspect of Nitric Oxide

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Endogenous NO, necessary for many physiological functions, is sometimes overproduced in inflammation and therefore carcinogenic, however no clear evidence has been reported. In this study, we obtained important data to answer this essential question.1. Oxanine (Oxa), a damaged base generated from Gua by NO-or HNO2-induced nitrosative deamination, has been considered as a mutagen-potent lesion. In this study, for exploring more detailed properties of Oxa, large-scale preparation of Oxa-containing DNA oligomers (Oxa-ODN) was developed: 2'-deoxynucleoside of Oxa (deoxyoxanosine, dOxo) obtained from dGuo by HNO2-nitrosation was subjected to 5'-0-selective tritylation (yield of DMT-dOxo, 70%). Subsequently DMT-dOxo was converted by conventional phosphoramidation to DMT-dOxo-amidite (yield, 72.5%). The amidite was used for synthesizing Oxa-ODNs: The coupling yields for Oxa incorporation and the total synthesis of 25mer DNA were over 93 and 85 %, respectively.2. Using DNA oligomers with or wi … More thout dOxo as templates and primers, DNA polymerase chain elongation was investigated and we found that in the opposite site to Oxa, T and C are incorporated almost equally, indicating that Oxa is mutagenic.3. We performed screening for the base-excision repair (BER) system to find no enzymic activity for the excision of Oxa, and revealed that Oxa-polyamine adduct is repaired by the nucleotide excision and recombination repair system, indicative of the cellular Oxa formation and that other DNA-relevant enzymes such as ligase and restriction enzymes recognize Oxa as Gua.4. We also found that Oxa-recognizing BER enzymes cross-link with Oxa in the DNA duplex irreversibly and this activity is eliminated by heat, while histones binding DNA nonspecifically also crosslink Oxa in DNA duplexes although slowly. This unique crosslinking will be helpful for fishing Oxa-recognizing and-repairing enzymes.5. NMR analysis for the structure around Oxa in DNA is now being conducted to reveal the mechanism for such unique properties of Oxa. Less