title: Interferon-gamma-inducible murine macrophage nitric oxide synthase: studies on the mechanism of inhibition by imidazole agents.
abstract: Citrulline formation by the interferon-gamma/lipopolysaccharide-inducible murine macrophage nitric oxide synthase is inhibited reversibly by imidazole, 1-phenylimidazole, 4-phenylimidazole, and 2-phenylimidazole with IC50 values of 40 microM, 6 microM, 225 microM, and > 1 mM, respectively. 1-Phenylimidazole inhibited the maximal velocity of citrulline formation but did not alter the concentration of arginine providing half-maximal activity. 1-Phenylimidazole inhibited citrulline formation by the murine macrophage nitric oxide synthase competitively versus (6R)-5,6,7,8-tetrahydro-L-biopterin (THB) with a Ki value of 0.7 microM, but inhibited citrulline formation by Ca(2+)-calmodulin-dependent nitric oxide synthase from GH3 pituitary cells noncompetitively versus THB with a Ki value of 40 microM. Imidazole inhibited citrulline formation by the murine macrophage nitric oxide synthase noncompetitively versus THB with a Ki value of 48 microM. Neither imidazole nor 1-phenylimidazole inhibited the cytochrome c reductase activity of murine macrophage nitric oxide synthase at concentrations 100-fold higher than their IC50 values for inhibiting citrulline formation. The antifungal imidazoles miconazole, ketoconazole, and clotrimazole did not inhibit either citrulline formation or cytochrome c reduction by murine macrophage nitric oxide synthase at concentration as high as 200 microM. Ca(2+)-calmodulin-dependent nitric oxide synthase from GH3 pituitary cells exhibited a Kact for THB of 80 nM, while the inducible murine macrophage nitric oxide synthase exhibited a Kact of 8 microM.
authors.affiliation: Department of Pharmacology, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854.
authors.forename: D J
authors.initials: DJ
authors.lastname: Wolff
authors.forename: B J
authors.initials: BJ
authors.lastname: Gribin
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D004790:Enzyme Induction; D007093:Imidazoles / Q000494:pharmacology*; D007371:Interferon-gamma / Q000494:pharmacology*; D007700:Kinetics; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000201:enzymology*; D051379:Mice; D019001:Nitric Oxide Synthase; D013329:Structure-Activity Relationship
chemical_list: D007093:Imidazoles; D008070:Lipopolysaccharides; C037738:1-phenylimidazole; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases