title: Cytochrome P4502A-mediated coumarin 7-hydroxylation and testosterone hydroxylation in mouse and rat lung.
abstract: Pulmonary coumarin 7-hydroxylase, testosterone hydroxylase and other P450-mediated activities were compared in the mouse and rat. Coumarin 7-hydroxylase activity was 20 pmol/mg/min. in mouse and 4 pmol/mg/min. in rat lung microsomes. Liver values were 180 (mouse) and 1 (rat) pmol/mg/min. Km values of rat and mouse lung coumarin 7-hydroxylase were about 1 microM whereas the rat liver Km value was > 100 microM. Phenobarbital and 3-methylcholanthrene did not affect rat lung (or liver) coumarin 7-hydroxylase activity. Anti-Cyp2a-5 antibody effectively inhibited mouse and rat lung coumarin 7-hydroxylase and testosterone 15 alpha-hydroxylations but failed to block these activities in the rat liver. In immunoblot analysis anti-Cyp2a-5 antibody recognized the 50-kDa Cyp2a-4/5 protein in mouse lung microsomes. A P450 protein co-migrating with Cyp2a-5 was also detected in rat lung microsomes. Cyp2a-5 cDNA probe hybridized with a 1.8-kb mRNA species in rat lung RNA fraction. The hybridization signal was not increased by 3-methylcholanthrene or phenobarbital. These data suggest that the mouse lung expresses Cyp2a-5 which differs from the liver enzyme only in its regulation and that the rat lung contains a P450 isoform(s) belonging to the 2A subfamily which may be orthologous with the mouse Cyp2a-4/5 catalyzing coumarin 7-hydroxylase and testosterone 15 alpha-hydroxylase activities. The recently reported rat lung CYP2A3 (Kimura et al.) gene product is a candidate for the observed coumarin 7-hydroxylase activity in the rat lung.
authors.affiliation: Department of Pharmacology and Toxicology, University of Kuopio, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Honkakoski
authors.forename: J
authors.initials: J
authors.lastname: Mäenpää
authors.forename: J
authors.initials: J
authors.lastname: Leikola
authors.forename: M
authors.initials: M
authors.lastname: Pasanen
authors.forename: R
authors.initials: R
authors.lastname: Juvonen
authors.forename: M A
authors.initials: MA
authors.lastname: Lang
authors.forename: O
authors.initials: O
authors.lastname: Pelkonen
authors.forename: H
authors.initials: H
authors.lastname: Raunio
mesh_terms: D015660:7-Alkoxycoumarin O-Dealkylase / Q000378:metabolism; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D015152:Blotting, Northern; D015153:Blotting, Western; D003001:Cloning, Molecular; D065637:Cytochrome P-450 CYP2A6; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D015342:DNA Probes; D004591:Electrophoresis, Polyacrylamide Gel; D066298:In Vitro Techniques; D007700:Kinetics; D008168:Lung / Q000201:enzymology*; D008297:Male; D051379:Mice; D008811:Mice, Inbred DBA; D008861:Microsomes / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D012313:RNA / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D013250:Steroid Hydroxylases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D015342:DNA Probes; D012313:RNA; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; D015660:7-Alkoxycoumarin O-Dealkylase; C585519:Cyp2a3 protein, rat; D001189:Aryl Hydrocarbon Hydroxylases; D065637:Cytochrome P-450 CYP2A6; C050356:steroid 15-alpha-hydroxylase