Ubiquinone redox cycle as a cellular antioxidant defense system.
Ubiquinone (UQ) reductase responsible for reduction of non-mitochondrial UQ was investigated in rats toward demonstrating an antioxidant role of UQ. In the liver, most of cellular UQ-10 reductase activity was attributable to a novel NADPH-UQ reductase in cytosol. The enzyme was not inhibited by dicumarol and rotenone, and had a Km of 19 microM for NADPH and 307 microM for NADH at the optimum pH 7.4. The enzyme was purified 300-fold to apparent homogeneity from the liver cytosol by an affinity chromatographic method. The purified enzyme reduced UQ-10 in lecithin liposomes, and protected the liposomes from lipid peroxidation. Furthermore, supplementation of rats with UQ-10 was observed to increase the enzyme level in their livers without affecting levels of other antioxidant factors. The observations suggested that cytosolic NADPH-UQ reductase is responsible for cellular UQ redox cycle as an endogenous antioxidant.
Kishi
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T
Faculty of Pharmaceutical Science, Kobe Gakuin University, Japan. kishi@pharm.kobegakuin.ac.jp
Takahashi
T
T
Usui
A
A
Okamoto
T
T
D000818:Animals; D000968:Antimycin A / Q000494:pharmacology; D000975:Antioxidants / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D001728:Dicumarol / Q000494:pharmacology; D042967:Electron Transport Complex I; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D008956:Models, Chemical; D009243:NAD / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D015388:Organelles / Q000201:enzymology; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D012402:Rotenone / Q000494:pharmacology; D014451:Ubiquinone / Q000737:chemistry / Q000378:metabolism*
D000975:Antioxidants; D012402:Rotenone; D009243:NAD; D014451:Ubiquinone; D009249:NADP; D000968:Antimycin A; D001728:Dicumarol; D009247:NADH, NADPH Oxidoreductases; D042967:Electron Transport Complex I