| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Takayuki Kobe Gakuin University, Faculty of Pharmaceutical Sciences, Research Associate, 薬学部, 助手 (40216726)
OKAMOTO Tadashi Kobe Gakuin University, Faculty of Pharmaceutical Sciences, Assistant professor, 薬学部, 講師 (80194398)
MORI Koichi Kobe Gakuin University, Faculty of Pharmaceutical Sciences, Associate professor, 薬学部, 助教授 (20098487)
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| Research Abstract |
In rat, ubiquinone (UQ) reducing activity was found to be attributable to a novel NADPHUQ reductase in cytosol. Then, the enzyme was purified 300-fold from liver cytosol by a chromatographic method using heparin- and hydroxyapatite affinity columns. The purified protein had a Km of 20.6 mu M for NADPH and 312 mu M for NADH at the optimum pH 7.4 and was not inhibited by 5 mu M dicumarol and 10 mu M rotenone, inhibitors of DT-diaphorase and mitochondrial NADH-UQ oxidoreductase, respectively. The enzyme also reduced UQ-1O in lecithin liposomes and UQ-9 in rat subcellular membranes, and protected the membranes from lipid peroxidation. Furthermore, rats fed on UQ-10 had an increased activity of the enzyme in livers, and were resistant to radical-induced hepatotoxicity by menadione, H_2 and CCl_4. The observations suggested that cytosolic NADPH-UQ reductase is the responsible enzyme for cellular UQ redox cycle as an endogenous antioxidant.
Endurance exercise by a bicycle ergometer of healthy, male subjects, which reported1y produces oxidative stress, also decreased their serum UQH_2-10 levels at maximal oxygen uptake, and the decreased UQH_2-10 were returned to normal level 30 min after the exercise. This observation suggested that UQH_2-1O also serves as an important antioxidant for the elimination of exercise-derived oxygen radicals in human.
In order to obtain pharmacologically active compounds, many ubiquinone analogues were synthesized chemically. The quantitative structure-activity relationships (QSAR) of 1, 4-benzoquinone derivatives on mitochondrial NADH-oxidase and succinate-oxidase and lipid peroxidation were carried out with 73 electronic parameters. The best three equations were obtained with three parameters. The QSAR results will be useful for the design of potential inhibitors of these enzymes and the lipid peroxidation.
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