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Issue title: The Fifth Conference of the International CoQ10 Association, Kobe 2007 – 50th anniversary of CoQ10 discovery
Article type: Research Article
Authors: Mukai, Kazuo | Tokunaga, Aiko | Itoh, Shingo | Kanesaki, Yu | Ouchi, Aya | Ohara, Keishi | Nagaoka, Shin-ichi | Abe, Kouichi
Affiliations: Department of Chemistry, Faculty of Science, Ehime University, Matsuyama, Japan | Eisai Co. Ltd., Tokyo, Japan
Note: [] Corresponding author: Tel.: +81 89 927 9588; Fax: +81 89 927 9590; E-mail: mukai@chem.sci.ehime-u.ac.jp
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).
Keywords: Free radicals, Vitamin E, ubiquinol-10, antioxidant activity, reaction rate, pH dependence, stopped-flow spectrophotometer, pK[TeX:] _{a}
Journal: BioFactors, vol. 32, no. 1-4, pp. 49-58, 2008
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