title: A unique tertiary amine N-oxide reduction system composed of quinone reductase and heme in rat liver preparations.
abstract: The results of this study show the quinone-dependent reduction of tertiary amine N-oxides to the corresponding tertiary amines by rat liver preparations. The reduction of imipramine N-oxide to imipramine mediated by liver mitochondria, microsomes, and cytosol proceeded in the presence of both NAD(P)H and menadione under anaerobic conditions. When menadione was replaced with 1, 4-naphthoquinone or 9,10-anthraquinone, similar results were obtained in the cytosolic reduction. The quinone-dependent reducing activity in liver cytosol was inhibited by dicumarol and carbon monoxide. This result suggested that the activity is caused by DT-diaphorase, a cytosolic quinone reductase, and hemoproteins in liver cytosol. In fact, catalase and hemoglobin showed the ability to reduce imipramine N-oxide when supplemented with DT-diaphorase. The hemoproteins also exhibited the N-oxide reductase activity with reduced menadione, menadiol. The N-oxide reductase activity of the hemoproteins was also exhibited with 1,4-dihydroxynaphthalene, 1,4,9, 10-tetrahydroxyanthracene, or 1,4-dihydroxy-9,10-anthraquinone. Furthermore, hematin revealed a significant N-oxide-reducing activity in the presence of menadiol. The reduction appears to proceed in two steps. The first step is reduction of menadione to menadiol by a quinone reductase with NADPH or NADH. The second step is nonenzymatic reduction of tertiary amine N-oxides to tertiary amines by menadiol, catalyzed by the heme group of hemoproteins. Cyclobenzaprine N-oxide and brucine N-oxide were also transformed similarly to the corresponding amine by the quinone-dependent reducing system.
authors.affiliation: Institute of Pharmaceutical Science, Hiroshima University School of Medicine, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8551, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kitamura
authors.forename: K
authors.initials: K
authors.lastname: Sugihara
authors.forename: K
authors.initials: K
authors.lastname: Tatsumi
mesh_terms: D000818:Animals; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D006168:Guinea Pigs; D006418:Heme / Q000378:metabolism*; D007099:Imipramine / Q000031:analogs & derivatives* / Q000378:metabolism; D008099:Liver / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D051379:Mice; D008862:Microsomes, Liver / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar
chemical_list: D006418:Heme; C002921:imipramine N-oxide; D016660:NAD(P)H Dehydrogenase (Quinone); D007099:Imipramine