Generation and elimination of 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate, a mutagenic substrate for DNA synthesis, in human cells.
8-Oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) is a potent mutagenic substrate for DNA synthesis. The present study deals with generation and degradation of 8-oxo-dGTP in the nucleotide pool of human cells. (1) 8-Oxo-dGTP can be generated not only by direct oxidation of dGTP but also by phosphorylation of 8-oxo-dGDP by nucleoside diphosphate kinase. (2) 8-Oxo-dGTP is rapidly degraded to 8-oxo-dGMP by cellular 8-oxo-dGTPase activity. 8-Oxo-dGMP thus produced cannot be rephosphorylated; guanylate kinase, which phosphorylates both GMP and dGMP to the corresponding nucleoside diphosphates, is totally inactive for 8-oxo-dGMP. (3) 8-Oxo-dGMP is further degraded to 8-oxo-deoxyguanosine by a nucleotidase. The enzyme was partially purified from an extract of human Jurkat cells, and the mode of action was elucidated. 8-Oxo-dGMP is the most preferred substrate of the enzyme, and other nucleoside monophosphates are cleaved at significantly lower rates: Km for 8-oxo-dGMP is 10 times lower than that for dGMP, the second best substrate for the enzyme. The enzyme appears to convert 8-oxo-dGMP, which accumulates in the cellular nucleotide pool, to a form readily excretable to the cell exterior.
Hayakawa
H
H
Department of Biochemistry, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Taketomi
A
A
Sakumi
K
K
Kuwano
M
M
Sekiguchi
M
M
D002474:Cell-Free System; D004247:DNA / Q000096:biosynthesis*; D003848:Deoxyguanine Nucleotides / Q000096:biosynthesis / Q000378:metabolism*; D051528:Guanylate Kinases; D006801:Humans; D009153:Mutagens / Q000378:metabolism*; D009701:Nucleoside-Diphosphate Kinase / Q000378:metabolism; D009703:Nucleoside-Phosphate Kinase / Q000378:metabolism; D009708:Nucleotidases / Q000378:metabolism; D010766:Phosphorylation; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
D003848:Deoxyguanine Nucleotides; D009153:Mutagens; C078206:8-oxodeoxyguanosine triphosphate; D004247:DNA; D009703:Nucleoside-Phosphate Kinase; D009701:Nucleoside-Diphosphate Kinase; D051528:Guanylate Kinases; C091540:8-oxo-dGMPase; D009708:Nucleotidases