Constitutive and inducible cytochromes P450 in rat lung mitochondria: Xenobiotic induction, relative abundance, and catalytic properties

The presence of xenobiotic-inducible CYP1A1, 2B1/2, and 3A1/2 in rat lung m itochondria was investigated using mitochondrial preparations of defined pu rity. The mitochondrial P450 content in uninduced lung was 1.5-fold higher compared to microsomes. Administration of BNF induced the P450 contents by twofold in both mitochondrial and microsomal membrane fractions. BNF treatm ent induced EROD activity to about 40-fold in the microsomal fraction and 2 5-fold in the mitochondrial fraction. The microsomal induction was observed at 4 days of BNF treatment, while the mitochondrial induction required 10 days of treatment. Consistent with the activity profile, Western blot analy sis showed the presence of CYP1A1 antibody reactive protein only in lung mi tochondria from BNF-treated rats. BNF administration also caused a 50 to 80 % reduction in the CYP2B1/2-associated PROD and BROD activities and CYP3A1/ 2-associated ERND activity in both mitochondria and microsomes. There was a lso a parallel reduction in the antibody reactive CYP2B1/2 and 3A1/2 protei ns in both of these membrane fractions. Administration of DEX for 4 days in duced mitochondrial and microsomal ERND activity by 1.7- and 2.5-fold, resp ectively. Mitochondrial EROD activity was inhibited by antibodies to P450MT 2, as well as Adx, but not by antibody against P450 reductase, indicating t he :mitochondrial localization of CYP1A1. Protease protection and alkaline extraction experiments indicated that CYP1A1 associated with lung mitochond ria is localized inside the inner membrane and exists as a membrane extrins ic protein. In summary, this is probably the first report of inducible P450 s in rat lung mitochondria, and our results suggest a possible functional r ole for these mitochondrial enzymes in xenobiotic metabolism. (C) 1999 Acad emic Press.