title: 2-ethynylnaphthalene as a mechanism-based inactivator of the cytochrome P-450 catalyzed N-oxidation of 2-naphthylamine.
abstract: Since the N-oxidation of several carcinogenic arylamines has been shown to be catalyzed preferentially by cytochrome P-450IA2 in several species, homologous ethynyl-substituted aromatic hydrocarbons, 2-ethynylnaphthalene, 1-ethynylnaphthalene, and 2-ethynylfluorene, were synthesized and examined as potential mechanism-based inactivators of this monooxygenase. By use of 2-naphthylamine, whose N-oxidation was known to be selectively catalyzed by rat cytochrome P-450ISF-G (P-450IA2), and hepatic microsomes from isosafrole-treated rats, each of these ethynyl derivatives was found to be strongly inhibitory at concentrations of 1 and 10 microM. However, only inhibition by 2-ethynylnaphthalene was significantly enhanced by prior incubation with the microsomal system. The inactivation of 2-naphthylamine N-oxidation was found to be NADPH- and time-dependent and to follow pseudo-first-order kinetics, demonstrating that 2-ethynylnaphthalene is a potent mechanism-based inactivator of the enzymatic activity. The extrapolated kinactivation and KI were 0.23 min-1 and 8 microM, respectively. By use of 2-aminofluorene, whose N-oxidation was known to be catalyzed by both cytochromes P-450ISF-G and P-450 beta NF-B (P-450IA1), and the purified enzymes in a reconstituted system, both 2-ethynylnaphthalene and 1-ethynylnaphthalene were found to be strongly inhibitory. However, 2-ethynylnaphthalene was a more potent inhibitor of the purified P-450ISF-G than of P-450 beta NF-B; and it was also found to be a more potent inhibitor of P-450ISF-G than was 1-ethynylnaphthalene.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: National Center for Toxicological Research, Jefferson, Arkansas 72079.
authors.forename: G J
authors.initials: GJ
authors.lastname: Hammons
authors.forename: W L
authors.initials: WL
authors.lastname: Alworth
authors.forename: N E
authors.initials: NE
authors.lastname: Hopkins
authors.forename: F P
authors.initials: FP
authors.lastname: Guengerich
authors.forename: F F
authors.initials: FF
authors.lastname: Kadlubar
mesh_terms: D015081:2-Naphthylamine / Q000378:metabolism*; D000818:Animals; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005449:Fluorenes / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009249:NADP / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology*; D010084:Oxidation-Reduction; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D005449:Fluorenes; D009281:Naphthalenes; C065012:2-ethynylnaphthalene; C012177:2-aminofluorene; D009249:NADP; D003577:Cytochrome P-450 Enzyme System; D015081:2-Naphthylamine