Sulphotransferase-mediated covalent binding of the carcinogen 7,12-dihydroxymethylbenz[a]anthracene to calf thymus DNA and its inhibition by glutathione transferase.
The carcinogen, 7,12-dihydroxymethylbenz[a]anthracene (DHBA), bound covalently through its 7-methylene carbon to calf thymus DNA via DHBA 7-sulphate, a regiospecifically formed, reactive metabolite, when incubated with rat liver cytosol in the presence of 3'-phosphoadenosine 5'-phosphosulphate (PAPS). The hydroxysteroid sulphotransferase inhibitor, dehydroepiandrosterone sulphate, strongly retarded the covalent binding of DHBA to DNA as well as the DHBA 7-sulphate formation from DHBA in the biological system, while pentachlorophenol and dichloronitrophenol showed little effect on these reactions. DHBA 7-sulphate was a good substrate for rat liver cytosolic glutathione (GSH) transferases, so that the PAPS-dependent covalent binding of DHBA to DNA could be markedly retarded in the presence of GSH with concomitant formation of a significant amount of the stable conjugate, S-(12-hydroxymethylbenz[a]anthracen-7-yl)methylglutathione. From DNA, incubated with DHBA in the presence of the hepatic cytosol and PAPS as well as with DHBA 7-sulphate alone, two purine base adducts were isolated after hydrolysis. The purine base adducts accounted for 70% of the total covalent binding of the carcinogen or its 7-sulphate to the nucleic acid and were identified with synthetic specimens as N6-(12-hydroxymethylbenz[a]anthracen-7-yl)-methyladenine and N2-12-hydroxymethylbenz[a]anthracen-7-yl)-methylguanine. The ratio of the adenine to guanine adducts was 1:2.5 with DNA, incubated with DHBA in the presence of hepatic cytosol and PAPS as well as with various concentrations of DHBA 7-sulphate.
Watabe
T
T
Hiratsuka
A
A
Ogura
K
K
D000818:Animals; D001551:Benz(a)Anthracenes / Q000378:metabolism*; D002273:Carcinogens / Q000378:metabolism*; D002417:Cattle; D003600:Cytosol / Q000201:enzymology; D004247:DNA / Q000378:metabolism*; D005978:Glutathione / Q000494:pharmacology; D005982:Glutathione Transferase / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D051381:Rats; D013466:Sulfurtransferases / Q000378:metabolism*; D013950:Thymus Gland
D001551:Benz(a)Anthracenes; D002273:Carcinogens; C046810:7,12-dihydroxymethylbenz(a)anthracene; D004247:DNA; D005982:Glutathione Transferase; D013466:Sulfurtransferases; D005978:Glutathione