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J Biol Chem, Vol. 275, Issue 16, 12326-12330, April 21, 2000

Accumulation of Adenine DNA Glycosylase-sensitive Sites in Human Mitochondrial DNA^*

Kenichi Miyako, Chihiro Takamatsu^§, Shuyo Umeda^§, Tatsurou Tajiri^¶, Masato Furuichi^¶, Yusaku Nakabeppu^¶, Mutsuo Sekiguchi^**, Naotaka Hamasaki^§, Koichiro Takeshige, and Dongchon Kang^§

From the Departments of  Biochemistry and ^§ Clinical Chemistry and Laboratory Medicine, Kyushu University Graduate School of Medical Sciences, the ^¶ Department of Biochemistry, Medical Institute of Bioregulation, Kyushu University,  Core Research for Evolutional Science and Technology, Japan Science and Technology Corp., Fukuoka 812-8582, and the ^** Department of Biology, Fukuoka Dental College, Fukuoka 814-0193, Japan

The mitochondrial respiratory chain inevitably produces reactive oxygen species as byproducts of aerobic ATP synthesis. Mitochondrial DNA (mtDNA), which is located close to the respiratory chain, is reported to contain much more 8-oxoguanine (8-oxoG), an oxidatively modified guanine base, than nuclear DNA. Despite such a high amount of 8-oxoG in mtDNA (1-2 8-oxoG/10⁴ G), mtDNA is barely cleaved by an 8-oxoG DNA glycosylase or MutM, which specifically excises 8-oxoG from a C:8-oxoG pair. We find here that about half of human mtDNA molecules are cleaved by another 8-oxoG-recognizing enzyme, an adenine DNA glycosylase or MutY, which excises adenine from an A:8-oxoG pair. The cleavage sites are mapped to adenines. The calculated number of MutY-sensitive sites in mtDNA is approximately 1.4/10⁴ G. This value roughly corresponds with the electrochemically measured amount of 8-oxoG in mtDNA (2.2/10⁴ G), raising the possibility that 8-oxoG mainly accumulates as an A:8-oxoG pair.

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