caa a22 4500 397555229 CHVBK 20180308164759.0 cr unu---uuuuu 161202e199602 xx s 000 0 eng 10.1093/oxfordjournals.jbchem.a021232 doi (NATIONALLICENCE)oxford-10.1093/oxfordjournals.jbchem.a021232 Characterization of NADPH-Dependent Ubiquinone Reductase Activity in Rat Liver Cytosol: Effect of Various Factors on Ubiquinone-Reducing Activity and Discrimination from Other Quinone Reductases [Elektronische Daten] [Takayuki Takahashi, Tadashi Okamoto, Takeo Kishi] Cytosolic NADPH-dependent ubiquinone reductase (NADPH-UQ reductase) accounted for about 68% of the total ubiquinone (UQ) reductase activity in rat liver homogenate [Takahashi, T. et al. (1995) Biochenu J. 309,883-890]. We investigated the effects of various factors on this enzyme activity in rat liver cytosol with the aim of elucidating its physiological roles. The NADPH-UQ reductase in rat liver cytosol catalyzed the reduction of UQ to UQH2 with concomitant oxidation of equimolar NADPH. The optimal pH was around 7.4, and the optimal temperatures were about 28°C for NADH and about 37°C for NADPH. NADH, deamino NADH, and deamino NADPH were much less active hydrogen donors than NADPH, whereas reduced nicotinamide mononucleotide, ascorbate, erythor-bate, reduced glutathione, and cysteine were inactive. As the hydrogen acceptor, UQ-9 had the highest Vmax/Km among the long-chain UQ homologues tested. FAD and FMN stimulated the activity. Anionic detergents, Mg2+ and Sr2+ also enhanced the activity. Rotenone, malonic acid, antimycin A, and KCN, which inhibit mitochondrial and microsomal electron transfer enzymes, superoxide dismutase, and acetylated cytochrome c had no effect on the NADPH-UQ reductase activity. These results indicated that the NADPH-UQ reductase in rat liver cytosol is a flavoprotein that reduces UQ-10 by a two-electron reduction mechanism and is distinguishable from known microsomal and mitochondrial enzymes, as well as DT-diaphorase [EC 1.6.99.2]. © by the Journal of Biochemistry Regular Papers nationallicence cytosol nationallicence liver nationallicence NADPH ubiquinone reductase nationallicence ubiquinol nationallicence ubiquinone nationallicence Takahashi Takayuki Kobe Gakuin University, Nishi-ku, Kobe 651-21 aut Okamoto Tadashi Kobe Gakuin University, Nishi-ku, Kobe 651-21 aut Kishi Takeo Kobe Gakuin University, Nishi-ku, Kobe 651-21 aut The Journal of Biochemistry Oxford University Press 119/2(1996-02), 256-263 0021-924X 119:2<256 1996 119 jbchem https://doi.org/10.1093/oxfordjournals.jbchem.a021232 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1093/oxfordjournals.jbchem.a021232 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Takahashi Takayuki Kobe Gakuin University, Nishi-ku, Kobe 651-21 aut NATIONALLICENCE 700 1- Okamoto Tadashi Kobe Gakuin University, Nishi-ku, Kobe 651-21 aut NATIONALLICENCE 700 1- Kishi Takeo Kobe Gakuin University, Nishi-ku, Kobe 651-21 aut NATIONALLICENCE 773 0- The Journal of Biochemistry Oxford University Press 119/2(1996-02), 256-263 0021-924X 119:2<256 1996 119 jbchem Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford