Biofactors - Volume 32, issue 1-4

Article Type: Other

Citation: BioFactors, vol. 32, no. 1-4, pp. 1-1, 2008

Article Type: Other

Citation: BioFactors, vol. 32, no. 1-4, pp. 3-3, 2008

Authors: Crane, Frederick L.

Article Type: Research Article

Abstract: In the 50 years since the identification of coenzyme Q as an electron carrier in mitochondria, it has been identified with diverse and unexpected functions in cells. Its discovery came as a result of a search for electron carriers in mitochondria following the identification of flavin and cytochromes by Warburg, Keilin, Chance and others. As a result of investigation of membrane lipids at D.E. Green's laboratory at University of Wisconsin coenzyme Q was identified as the …electron carrier between primary flavoprotein dehydrogenases and the cytochromes. Then Peter Mitchell identified the role of transmembrane proton transfer as a basis for ATP synthesis. The general distribution of coenzyme Q in all cell membranes then led to the recognition of a role as a primary antioxidant. The protonophoric function was extended to acidification of Golgi and lysosomal vericles. A further role in proton release through the plasma membrane and its relation to cell proliferation has not been fully developed. A role in generation of H_{2} 0_{2} as a messenger for hormone and cytokine action is indicated as well as prevention of apoptosis by inhibition of ceramide release. Identification of the genes and proteins required for coenzyme Q synthesis has led to a basis for defining deficiency. For 50 years Karl Folkers has led the search for deficiency and therapeutic application. The development of large scale production, better formulation for uptake, and better methods for analysis have furthered this search. The story isn't over yet. Questions remain about effects on membrane structure, breakdown and control of cellular synthesis and uptake and the basis for therapeutic action. Show more

Citation: BioFactors, vol. 32, no. 1-4, pp. 5-11, 2008

Authors: Ohnishi, Tomoko | Ohnishi, S. Tsuyoshi | Shinzawa-Ito, Kyoko | Yoshikawa, Shinya

Article Type: Research Article

Abstract: Coenzyme Q_{10} (which is also designated as CoQ_{10} , ubiquinone-10, UQ_{10} , CoQ, UQ or simply as Q) plays an important role in energy metabolism. For NADH-Q oxidoreductase (complex I), Ohnishi and Salerno proposed a hypothesis that the proton pump is operated by the redox-driven conformational change of a Q-binding protein, and that the bound form of semiquinone (SQ) serves as its gate [FEBS Letters 579 (2005) 45–55]. This was based on …the following experimental results: (i) EPR signals of the fast-relaxing SQ anion (designated as Q_{Nf}^{˙ -} ) are observable only in the presence of the proton electrochemical potential (Δμ_{H}^{+} ); (ii) iron-sulfur cluster N2 and Q_{Nf}^{˙ -} are directly spin-coupled; and (iii) their center-to-center distance was calculated as 12Å, but Q_{Nf}^{˙ -} is only 5Å deeper than N2 perpendicularly to the membrane. After the priming reduction of Q to Q_{Nf}^{˙ -} , the proton pump operates only in the steps between the semiquinone anion (Q_{Nf}^{˙ -} ) and fully reduced quinone (QH_{2} ). Thus, by cycling twice for one NADH molecule, the pump transports 4H^{+} per 2e^{-} . This hypothesis predicts the following phenomena: (a) Coupled with the piericidin A sensitive NADH-DBQ or Q_{1} reductase reaction, Δμ_{H}^{+} would be established; (b) Δμ_{H}^{+} would enhance the SQ EPR signals; and (c) the dissipation of Δμ_{H}^{+} with the addition of an uncoupler would increase the rate of NADH oxidation and decrease the SQ signals. We reconstituted bovine heart complex I, which was prepared at Yoshikawa's laboratory, into proteoliposomes. Using this system, we succeeded in demonstrating that all of these phenomena actually took place. We believe that these results strongly support our hypothesis. Show more

Keywords: NADH-CoQ oxidoreductase (complex I), proteoliposome, reconstitution, membrane potential, iron-sulfur cluster N2, semiquinone, EPR

Citation: BioFactors, vol. 32, no. 1-4, pp. 13-22, 2008

Authors: Mustafa, Golam | Ishikawa, Yoshinori | Kobayashi, Kazuo | Migita, Catharina T. | Tagawa, Seiichi | Yamada, Mamoru

Article Type: Research Article

Abstract: Membrane-bound glucose dehydrogenase (mGDH) is a single integral protein in the respiratory chain in Escherichia coli which oxidizes D-glucose and feeds electrons to ubiquinol oxidase via bulk ubiquinone (UQ). mGDH contains a bound UQ, CoQ_{8} , for its intramolecular electron transfer in addition to pyrroloquinoline quinone (PQQ) as a coenzyme. Pulse radiolysis analysis revealed that the bound UQ exists very close to PQQ at a distance of 11–13 Å Studies on mGDH mutants with substitutions …for amino acid residues around PQQ showed that Asp-466 and Lys-493, which are crucial for catalytic activity, interact with bound UQ. Based on these findings, we propose that the bound UQ is involved in the catalytic reaction in addition to the intramolecular electron transfer in mGDH. Show more

Keywords: Glucose dehydrogenase, pyrroloquinoline quinone, ubiquinone, intramolecular electron transfer

Citation: BioFactors, vol. 32, no. 1-4, pp. 23-29, 2008

Authors: Fato, Romana | Bergamini, Christian | Leoni, Serena | Lenaz, Giorgio

Article Type: Research Article

Abstract: Mitochondrial reactive oxygen species (ROS) are mainly produced by the respiratory chain enzymes. The sites for ROS production in mitochondrial respiratory chain are normally ascribed to the activity of Complex I and III. The presence of specific inhibitors modulates reactive oxygen species production in Complex I: inhibitors such as rotenone induce a strong ROS increase, while inhibitors such as stigmatellin prevent it. We have investigated the effect of hydrophilic quinones on Complex I ROS production in …presence of different inhibitors. Some short chain quinones are Complex I inhibitors (CoQ_{2} , idebenone and its derivatives), while CoQ_{1} , decylubiquinone~ (DB) and duroquinone (DQ) are good electron acceptors from Complex I. Our results show that the ability of short chain quinones to induce an oxidative stress depends on the site of interaction with Complex I and on their physical-chemical characteristics. We can conclude that hydrophilic quinones may enhance oxidative stress by interaction with the electron escape sites on Complex I while more hydrophobic quinones can be reduced only at the physiological quinone reducing site without reacting with molecular oxygen. Show more

Keywords: Complex I, ROS, Complex I inhibitors, short chain quinones, submitochondrial particles

Citation: BioFactors, vol. 32, no. 1-4, pp. 31-39, 2008

Authors: Imada, Isuke | Sato, Eisuke F. | Kira, Yukimi | Inoue, Masayasu

Article Type: Research Article

Abstract: Effect of CoQ compounds (Qs) on reactive oxygen (ROS) generation by mitochondrial complex I was studied using rat liver mitochondria and chemiluminescence probe L012. Kinetic analysis revealed that short chain Qs, such as Q_{2} and idebenone enhanced ROS generation by mitochondrial NADH oxidase system by a succinate-inhibitable mechanism. Lipid peroxidation in mitochondrial membranes induced by NADH and iron was inhibited by short chain Qs. The inhibitory activity was enhanced by co-oxidation of …succinate as determined by chemiluminescence method and by electron spin resonance spectroscopy. These results suggested that the reduced form of short chain Qs inhibited mitochondrial ROS generation and lipid peroxidation. Show more

Keywords: Coenzyme Q, idebenone, complex I, reactive oxygen species, lipid peroxidation, oxidative stress

Citation: BioFactors, vol. 32, no. 1-4, pp. 41-48, 2008

Authors: Mukai, Kazuo | Tokunaga, Aiko | Itoh, Shingo | Kanesaki, Yu | Ouchi, Aya | Ohara, Keishi | Nagaoka, Shin-ichi | Abe, Kouichi

Article Type: Research Article

Abstract: Detailed kinetic studies have been performed for the reaction of aroxyl (ArO•) radical with vitamin E (α-, β-, γ-, δ-tocopherol, TocH), ubiquinol-10, and related antioxidants in micellar solution, using a stopped-flow spectrophotometer. The second-order reaction rates (k_{s} ) obtained increased in the order of hydroquinone < tocol<δ-TocH<ubiquinol-0<γ-TocH∼ β-TocH<ubiquinol-10<α-TocH at pH 4 ∼ 8. The antioxidants which have lower oxidation potentials (E_{p} ) showed higher reactivities. The reaction …rates obtained in micellar solution were pH dependent because of the dissociation of OH groups in the antioxidants. For instance, by comparing the k_{s} values with the mole fraction of each molecular form of ubiquinol-10, the reaction rate k_{s1} (1.21 × 10^{5} M^{-1} s^{-1} ) for undissociated form, k_{s2} (1.04 × 10^{6} M^{-1} s^{-1} ) for monoanion and k_{s3} (0 M^{-1} s^{-1} ) for dianion, and the pK_{a1} and pK_{a2} values (11.4 and 12.7) were determined. It was found that the relative ratio of k_{s} values (100:21:20:2.9) of α-, β-, γ-, δ-tocopherols in micellar dispersion has good correlation with the relative biological activities for rat fetal resorption, rat haemolysis, and chicken muscle dystrophy. The relative antioxidant activities of α-tocopherol and ubiquinol-10 have been discussed on the basis of the products of the k_{s} values and their concentrations in serum and several tissues (heart, muscle, liver, kidney, and brain). Show more

Keywords: Free radicals, Vitamin E, ubiquinol-10, antioxidant activity, reaction rate, pH dependence, stopped-flow spectrophotometer, pK_{a}

Citation: BioFactors, vol. 32, no. 1-4, pp. 49-58, 2008

Authors: Takahashi, Takayuki | Okuno, Masaaki | Okamoto, Tadashi | Kishi, Takeo

Article Type: Research Article

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. Show more

Keywords: Antioxidant, coenzyme Q, NADPH-CoQ reductase, rat liver, ubiquinol, zinc

Citation: BioFactors, vol. 32, no. 1-4, pp. 59-70, 2008

Authors: Bruge, Francesca | Virgili, Samantha | Cacciamani, Tiziana | Principi, Federica | Tiano, Luca | Littarru, Gian Paolo

Article Type: Research Article

Abstract: Two-electron reduction of quinones catalyzed by NAD(P)H:quinone oxidoreductase (NQO1) protects cells against oxidative stress and toxic quinones. In fact, low level of NQO1 activity is often associated with increased risk of developing different types of tumours and with toxic effects linked to environmental quinones. In a previous report we analyzed the relationship between the oxidative stress induced by UV radiation and CoQ_{10} content in Burkitt's lymphoma cell lines compared to …HL-60. The basal content of CoQ_{10} in Raji cells was slightly higher compared to HL-60. Moreover, after irradiation or ubiquinone supplementation in the medium, reduced CoQ_{10} levels were higher in Raji and Daudi cells compared to HL-60. In the present work, in order to inquire if NQO1 plays a role in the CoQ reducing capacity observed in the lymphoblastoid cell lines, we analyzed the transcription and translation products of this gene in Raji and Daudi cells, compared to cell lines possessing low and high NQO1 activity. The amount of transcripts of this gene in lymphoblastoid cells was comparable to that observed in HL-60 cells (low activity), as well as the level of two alternatively spliced mRNAs; one of which is described for the first time in this work. From the genotype analysis of polymorphisms C609T and C465T we observed that HL-60, Raji and Daudi cells were all heterozygous. Furthermore, NQO1 enzyme activity and protein synthesis in the cytosol of Raji and Daudi cells were undetectable. Therefore in Burkitt's lymphoma cell lines the NQO1 gene is not efficiently translated and this effect is not related to (C609T) polymorphism. Further studies will be necessary to find the enzyme responsible for CoQ_{10} reducing activity observed in lymphoma cell lines. On the other hand, this result suggests a careful re-evaluation of data concerning loss of NQO1 activity and polymorphisms in tumour cells. Show more

Keywords: Burkitt's lymphoma, coenzyme Q oxidoreductase, polymorphism, alternative splicing

Citation: BioFactors, vol. 32, no. 1-4, pp. 71-81, 2008