Affiliations: Laboratory of Biochemistry, Department of Health
Sciences and Social Pharmacy, Faculty of Pharmaceutical Sciences, Kobe Gakuin
University, Kobe, Japan | Cooperative Research Center of Life Sciences, Kobe
Gakuin University, Kobe, Japan
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 CoQ_{10} 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 CoQ_{10} reductases in the sensitivities to its
inhibitors and stimulators. Especially, Zn^{2+} was the most
powerful inhibitor for NADPH-CoQ reductase, but CoQ_{10}
reduction by the other CoQ_{10} reductases could not be
inhibited by Zn^{2+}. Furthermore, the reduction of the
CoQ_{9} incorporated into HeLa cells was also inhibited by
Zn^{2+} 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 CoQ_{9}
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.
Keywords: Antioxidant, coenzyme Q, NADPH-CoQ reductase, rat liver, ubiquinol, zinc
Journal: BioFactors, vol. 32, no. 1-4, pp. 59-70, 2008
