Sakumi K, Furuichi M, Tsuzuki T, Kakuma T, Kawabata S, Maki H, Sekiguchi M
Medical Institute of Bioregulation, Faculty of Science, Kyushu University, Fukuoka, Japan.
J Biol Chem. 1993 Nov 5;268(31):23524-30.
8-Oxoguanine (8-oxo-7, 8-dihydroguanine) is produced in DNA, as well as in nucleotide pools of cells, by active oxygen species normally formed during cellular metabolic processes. 8-Oxoguanine nucleotide can pair with cytosine and adenine nucleotides at almost equal efficiencies, and transversion mutation ensues. Human cells contain enzyme activity, which hydrolyzes 8-oxo-dGTP to 8-oxo-dGMP, and this enzyme is responsible for preventing misincorporation of 8-oxoguanine into DNA. We purified this particular human enzyme to physical homogeneity and determined a partial amino acid sequence. We then cloned the cDNA for human 8-oxo-dGTPase and examined its nucleotide sequence. The human protein comprises 156 amino acid residues and has some sequence homology with the Escherichia coli MutT protein, which has a distinct 8-oxo-dGTPase activity. When the human cDNA was expressed in E. coli mutT- mutant cells, there was a significant amount of 8-oxo-dGTPase activity. In such cells, the frequency of spontaneous mutation was greatly reduced. We propose that the human 8-oxo-dGTPase protects genetic information from the untoward effects of endogenous oxygen radicals.
8-氧代鸟嘌呤（8-氧代-7,8-二氢鸟嘌呤）在DNA以及细胞的核苷酸池中，由细胞代谢过程中正常形成的活性氧产生。8-氧代鸟嘌呤核苷酸能以几乎相同的效率与胞嘧啶和腺嘌呤核苷酸配对，从而导致颠换突变。人类细胞含有将8-氧代-dGTP水解为8-氧代-dGMP的酶活性，该酶负责防止8-氧代鸟嘌呤错误掺入DNA。我们将这种特定的人类酶纯化至物理纯，并确定了部分氨基酸序列。然后我们克隆了人类8-氧代-dGTP酶的cDNA并检测了其核苷酸序列。人类蛋白质由156个氨基酸残基组成，与具有独特8-氧代-dGTP酶活性的大肠杆菌MutT蛋白有一些序列同源性。当人类cDNA在大肠杆菌mutT -突变细胞中表达时，会有大量的8-氧代-dGTP酶活性。在这类细胞中，自发突变的频率大大降低。我们提出人类8-氧代-dGTP酶保护遗传信息免受内源性氧自由基的不良影响。
