title: Hepatic mitochondrial cytochrome P-450 system. Purification and characterization of two distinct forms of mitochondrial cytochrome P-450 from beta-naphthoflavone-induced rat liver.
abstract: We have purified two distinct isoforms of mitochondrial cytochrome P-450 from beta-naphthoflavone (beta-NF)-induced rat liver to greater than 85% homogeneity and characterized their molecular and catalytic properties. One of these isoforms showing an apparent molecular mass of 52 kDa is termed P-450mt1 and the second isoform with 54-kDa molecular mass is termed P-450mt2. Cytochrome P-450mt2 comigrates with similarly induced microsomal P-450c (the major beta-NF-inducible form) on sodium dodecyl sulfate-polyacrylamide gels and cross-reacts with polyclonal antibody monospecific for cytochrome P-450c. Cytochrome P-450mt2, however, represents a distinct molecular species since it failed to react with a monoclonal antibody to P-450c and produced V8 protease fingerprints different from P-450c. Cytochrome P-450mt1, on the other hand, did not show any immunochemical homology with P-450c or P-450mt2 as well as partially purified P-450 from control mitochondria. Electrophoretic comparisons and Western blot analysis show that both P-450mt1 and P-450mt2 are induced forms not present in detectable levels in control liver mitochondria. A distinctive property of mitochondrial P-450mt1 and P-450mt2 was that their catalytic activities could be reconstituted with both NADPH-cytochrome P-450 reductase as well as mitochondrial specific ferredoxin and ferredoxin reductase electron transfer systems, while P-450c showed exclusive requirement for NADPH-cytochrome P-450 reductase. Cytochromes P-450mt1 and P-450mt2 were able to metabolize xenobiotics like benzo(a)pyrene and dimethyl benzanthracene at rates only one-tenth with cytochrome P-450c. Furthermore, P-450mt1, P-450mt2, as well as partially purified P-450 from control liver, but not P-450c, showed varying activities for 25- and 26-hydroxylation of cholesterol and 25-hydroxylation of vitamin D3. These results provide evidence for the presence of at least two distinct forms of beta-NF-inducible cytochrome P-450 in rat hepatic mitochondria.
authors.affiliation: Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104.
authors.forename: H
authors.initials: H
authors.lastname: Raza
authors.forename: N G
authors.initials: NG
authors.lastname: Avadhani
mesh_terms: D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology*; D002845:Chromatography; D002852:Chromatography, Ion Exchange; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D017886:Durapatite; D004579:Electron Transport; D004790:Enzyme Induction; D005419:Flavonoids / Q000494:pharmacology*; D006882:Hydroxyapatites; D007527:Isoenzymes / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D019324:beta-Naphthoflavone
chemical_list: D001571:Benzoflavones; D005419:Flavonoids; D006882:Hydroxyapatites; D007527:Isoenzymes; D019324:beta-Naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D017886:Durapatite