title: NADPH-dependent coenzyme Q reductase is the main enzyme responsible for the reduction of non-mitochondrial CoQ in cells.
abstract: We purified an NADPH-dependent coenzyme Q reductase (NADPH-CoQ reductase) in rat liver cytosol and compared its enzymatic properties with those of the other CoQ10 reductases such as NADPH: quinone acceptor oxidoreductase 1 (NQO1), lipoamide dehydrogenase, thioredoxine reductase and glutathione reductase. NADPH-CoQ reductase was the only enzyme that preferred NADPH to NADH as an electron donor and was also different from the other CoQ10 reductases in the sensitivities to its inhibitors and stimulators. Especially, Zn2+ was the most powerful inhibitor for NADPH-CoQ reductase, but CoQ10 reduction by the other CoQ10 reductases could not be inhibited by Zn2+. Furthermore, the reduction of the CoQ9 incorporated into HeLa cells was also inhibited by Zn2+ in the presence of pyrithione, a zinc ionophore. Moreover, NQO1 gene silencing in HeLa cells by transfection of a small interfering RNA resulted in lowering of both the NQO1 protein level and the NQO1 activity by about 75%. However, this transfection did not affect the NADPH-CoQ reductase activity and the reduction of CoQ9 incorporated into the cells. These results suggest that the NADPH-CoQ reductase located in cytosol may be the main enzyme responsible for the reduction of non-mitochondrial CoQ in cells.
authors.affiliation: Laboratory of Biochemistry, Department of Health Sciences and Social Pharmacy, Faculty of Pharmaceutical Sciences, Kobe Gakuin University, Kobe, Japan. takahasi@pharm.kobegakuin.ac.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Takahashi
authors.forename: Masaaki
authors.initials: M
authors.lastname: Okuno
authors.forename: Tadashi
authors.initials: T
authors.lastname: Okamoto
authors.forename: Takeo
authors.initials: T
authors.lastname: Kishi
mesh_terms: D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D003600:Cytosol / Q000201:enzymology; D001728:Dicumarol / Q000494:pharmacology; D008058:Dihydrolipoamide Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008099:Liver / Q000201:enzymology*; D015636:Magnesium Chloride / Q000494:pharmacology; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010084:Oxidation-Reduction; D011725:Pyridines / Q000494:pharmacology; D011808:Quinone Reductases / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D012402:Rotenone / Q000494:pharmacology; D013871:Thiones / Q000494:pharmacology; D054481:Thioredoxin Reductase 1 / Q000378:metabolism; D014162:Transfection; D014451:Ubiquinone / Q000031:analogs & derivatives / Q000378:metabolism*; D017967:Zinc Compounds / Q000494:pharmacology
chemical_list: D002712:Chlorides; D011725:Pyridines; D013871:Thiones; D017967:Zinc Compounds; D015636:Magnesium Chloride; D012402:Rotenone; D014451:Ubiquinone; C008704:pyrithione; D001728:Dicumarol; C016837:zinc chloride; D009247:NADH, NADPH Oxidoreductases; C534775:NADPH-coenzyme Q reductase, rat; D011808:Quinone Reductases; D008058:Dihydrolipoamide Dehydrogenase; D054481:Thioredoxin Reductase 1; C024989:coenzyme Q10; D002211:Capsaicin