Binding of benzo[a]pyrene to DNA by cytochrome P-450 catalyzed one-electron oxidation in rat liver microsomes and nuclei.
To investigate whether cytochrome P-450 catalyzes the covalent binding of substrates to DNA by one-electron oxidation, the ability of both uninduced and 3-methylcholanthrene (MC) induced rat liver microsomes and nuclei to catalyze covalent binding of benzo[a]pyrene (BP) to DNA and formation of the labile adduct 7-(benzo[a]pyren-6-yl)guanine (BP-N7Gua) was investigated. This adduct arises from the reaction of the BP radical cation at C-6 with the nucleophilic N-7 of the guanine moiety. In the various systems studied, 1-9 times more BP-N7Gua adduct was isolated than the total amount of stable BP adducts in the DNA. The specific cytochrome P-450 inhibitor 2-[(4,6-dichloro-o-biphenyl)oxy]ethylamine hydrobromide (DPEA) reduced or eliminated BP metabolism, binding of BP to DNA, and formation of BP-N7Gua by cytochrome P-450 in both microsomes and nuclei. The effects of the antioxidants cysteine, glutathione, and p-methoxythiophenol were also investigated. Although cysteine had no effect on the microsome-catalyzed processes, glutathione and p-methoxythiophenol inhibited BP metabolism, binding of BP to DNA, and formation of BP-N7Gua by cytochrome P-450 in both microsomes and nuclei. The decreased levels of binding of BP to DNA in the presence of glutathione or p-methoxythiophenol are matched by decreased amounts of BP-N7Gua adduct and of stable BP-DNA adducts detected by the 32P-postlabeling technique. This study represents the first demonstration of cytochrome P-450 mediating covalent binding of substrates to DNA via one-electron oxidation and suggests that this enzyme can catalyze peroxidase-type electron-transfer reactions.
Cavalieri
E L
EL
Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha 68198-6805.
Rogan
E G
EG
Devanesan
P D
PD
Cremonesi
P
P
Cerny
R L
RL
Gross
M L
ML
Bodell
W J
WJ
D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism*; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004579:Electron Transport; D066298:In Vitro Techniques; D008099:Liver / Q000378:metabolism; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D015394:Molecular Structure; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains
D001564:Benzo(a)pyrene; D004247:DNA; D003577:Cytochrome P-450 Enzyme System