title: Enzymatic methylation of microsomal metabolites of benzo(a)pyrene.
abstract: These studies suggest that the microsomal metabolism of benzo(a)pyrene (BP) produces metabolites which can be methylated by the catechol-o-methyltransferase (COMT)/S-adenosylmethionine (SAM) enzyme/donor combination. Induced microsomes converted 12 to 15% of substrate BP to polar products. Approximately 0.06% of substrate BP was recovered as COMT/SAM-reactive substances. In tests for specificity, COMT/SAM was found to react with catechols, but not with dihydrodiols, quinones, a phenol, an epoxide, or 1,4-hydroquinone. Organic extracts of COMT/[14C]SAM incubations with BP were fractionated by high-performance liquid chromatography. The appearance of radiolabeled chromatographic bands required the presence of substrate BP, microsomes, and COMT/[14C]SAM. When the Ames mutagenesis assay was supplemented with COMT/SAM, a 36% reduction was observed in the number of revertant colonies induced by the microsomal oxidation of BP. In contrast, the mutagenic properties of 2-aminofluorene were not affected by COMT/SAM. These observations indicate that COMT/SAM does not generally inhibit mixed-function oxidase activity but rather reacts with substances which are activated by ring oxygenations.
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene; D001580:Benzopyrenes / Q000378:metabolism* / Q000494:pharmacology; D001711:Biotransformation; D002394:Catechol O-Methyltransferase / Q000378:metabolism* / Q000494:pharmacology; D002851:Chromatography, High Pressure Liquid; D008297:Male; D008745:Methylation; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011916:Rats, Inbred F344; D012436:S-Adenosylmethionine / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D001580:Benzopyrenes; D001564:Benzo(a)pyrene; D012436:S-Adenosylmethionine; D002394:Catechol O-Methyltransferase