title: Tunneling effect in regeneration reaction of vitamin E by ubiquinol.
abstract: A kinetic study of the regeneration reaction of vitamin E by ubiquinol was carried out by means of double-mixing stopped-flow spectroscopy. A substantial deuterium kinetic-isotope effect was observed on the second-order rate constant and the activation energy. In the regeneration reaction of alpha-tocopherol, deuteration of ubiquinol increased and decreased the activation energy and the second-order rate constant by 6.1 kJ/mol and a factor of 18.3, respectively. From this result, it is considered that proton tunneling plays an important role in the regeneration reaction of vitamin E by ubiquinol. The conditions under which the tunneling effect becomes an important factor were discussed in conjunction of our experimental results.
authors.affiliation: Department of Chemistry, Faculty of Science, Ehime University, Matsuyama 790-8577, Japan. oouchi@chem.sci.ehime-u.ac.jp
authors.forename: Aya
authors.initials: A
authors.lastname: Ouchi
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Nagaoka
authors.forename: Kazuo
authors.initials: K
authors.lastname: Mukai
mesh_terms: D003903:Deuterium / Q000737:chemistry; D007700:Kinetics; D011522:Protons; D013816:Thermodynamics; D014451:Ubiquinone / Q000031:analogs & derivatives* / Q000737:chemistry; D014810:Vitamin E / Q000737:chemistry*; D024502:alpha-Tocopherol / Q000737:chemistry
chemical_list: D011522:Protons; D014451:Ubiquinone; D014810:Vitamin E; D003903:Deuterium; D024502:alpha-Tocopherol; C003741:ubiquinol