title: Metabolism of phenanthrene by brown bullhead liver microsomes.
abstract: We have investigated the regio- and stereoselective metabolism of phenanthrene by the liver microsomes of brown bullhead (Ameriurus nebulosus), a bottom dwelling fish species. The liver microsomes from untreated and 3-methylcholanthrene (3-MC)-treated brown bullheads metabolized phenanthrene at a rate of 14.1 and 20.7 pmol/mg protein/min, respectively, indicating that the hydrocarbon is a rather poor substrate for bullhead liver microsomes contrary to what has been reported for rat liver microsomes. The major phenanthrene metabolites formed by liver microsomes from untreated and 3-MC-treated bullheads included benzo-ring 1,2-dihydrodiol (25.3 and 11.6%), K-region 9,10-dihydrodiol (9.6 and 9.6%), and phenols (40.5 and 54.5%). The 3,4-dihydrodiol represented a minor proportion of the total phenanthrene metabolites. The low proportion of the 9,10-dihydrodiol formed by both control and 3-MC-treated bullhead microsomes sharply contrasts the previous data reported for the corresponding rat liver microsomes which metabolized phenanthrene predominantly to its 9,10-dihydrodiol representing 76.6 and 67.1%, respectively of the total metabolites. Liver microsomes from 3-MC-treated bullheads, like rat liver microsomes, were more selective in their attack at the 1,2-position of the benzo-ring than at the 3,4-position of the benzo-ring. Phenanthrene 1,2-dihydrodiol and 3,4-dihydrodiol formed by liver microsomes from both control and 3-MC-treated bullheads consisted predominantly of their R,R enantiomer. Phenanthrene, compared with benzo[a]pyrene and chrysene, is metabolized by bullhead liver microsomal enzymes to its benzo-ring dihydrodiols with a relatively low degree of stereoselectivity.
authors.affiliation: Great Lakes Center for Environmental Research and Education, State University of New York College at Buffalo, Buffalo, NY 14222, USA.
authors.forename: Jyotsna
authors.initials: J
authors.lastname: Pangrekar
authors.forename: Panna L
authors.initials: PL
authors.lastname: Kole
authors.forename: Sangeet A
authors.initials: SA
authors.lastname: Honey
authors.forename: Subodh
authors.initials: S
authors.lastname: Kumar
authors.forename: Harish C
authors.initials: HC
authors.lastname: Sikka
mesh_terms: D000818:Animals; D002273:Carcinogens / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D007059:Ictaluridae / Q000378:metabolism*; D008748:Methylcholanthrene / Q000633:toxicity; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D008968:Molecular Conformation; D010616:Phenanthrenes / Q000737:chemistry / Q000378:metabolism* / Q000633:toxicity; D014874:Water Pollutants, Chemical / Q000378:metabolism* / Q000633:toxicity
chemical_list: D002273:Carcinogens; D010616:Phenanthrenes; D014874:Water Pollutants, Chemical; C031181:phenanthrene; D008748:Methylcholanthrene