title: Pulmonary microsomal cytochrome P-450 from 3-methylcholanthrene-treated hamsters: purification, characterization, and metabolism of benzo(a)pyrene.
abstract: A major form of pulmonary cytochrome P-450 (pulmonary P-450MC) was purified approximately 165-fold from lung microsomes of 3-methylcholanthrene (MC)-treated hamsters. The purified preparation contained 14.2 nmol of cytochrome P-450 (P-450) per mg protein and was essentially free from NADPH-cytochrome P-450 (cytochrome c)-reductase (NADPH-reductase) and epoxide hydrolase. Pulmonary P-450MC exhibits an absorption maximum at 446.5 nm in the difference spectrum of reduced hemoprotein-CO complex, and a low-spin state of ferric iron in the heme. By sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, the molecular weight of pulmonary P-450MC was estimated to be 56,000. In a reconstituted system, pulmonary P-450MC efficiently catalyzed benzo(a)pyrene (BP) hydroxylation, but showed low activities for 7-ethoxycoumarin O-deethylation and benzphetamine N-demethylation. In Ouchterlony double diffusion analysis, hamster pulmonary P-450MC reacted to the antibody prepared against rat hepatic P-450MC to form a faint precipitation line with a spur, indicating that the two P-450MCs have a common antigenic site but are not immunologically identical. When incubated with [14C]BP in a reconstituted system containing NADPH-reductase and epoxide hydrolase, hamster pulmonary P-450MC formed much higher amounts of BP diols, especially 7,8-diol, than were formed by rat pulmonary P-450MC.
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D006224:Cricetinae; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification* / Q000378:metabolism; D005779:Immunodiffusion; D007527:Isoenzymes / Q000302:isolation & purification* / Q000378:metabolism; D008168:Lung / Q000187:drug effects / Q000648:ultrastructure*; D008297:Male; D008647:Mesocricetus; D008748:Methylcholanthrene / Q000494:pharmacology*; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology*; D008970:Molecular Weight
chemical_list: D007527:Isoenzymes; D001564:Benzo(a)pyrene; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System