title: Reaction rates of α-tocopheroxyl radicals confined in micelles and in human plasma lipoproteins.
abstract: α-Tocopherol, the main component of vitamin E, traps highly reactive radicals which otherwise might react with lipids present in plasmatic lipoproteins or in cell membranes. The α-tocopheroxyl radicals generated by this process have also a pro-oxidant action which is contrasted by their reaction with ascorbate or by bimolecular self-reaction (dismutation). The kinetics of this bimolecular self-reaction were explored in solution such as ethanol, and in heterogeneous systems such as deoxycholic acid micelles and in human plasma. According to ESR measurements, the kinetic rate constant (2k(d)) of the bimolecular self-reaction of α-tocopheroxyl radicals in micelles and in human plasma was calculated to be of the order of 10(5) M(-1) s(-1) at 37 °C. This value was obtained considering that the reactive radicals are confined into the micellar pseudophase and is one to two orders of magnitude higher than the value we found in homogeneous phase. The physiological significance of this high value is discussed considering the competition between bimolecular self-reaction and the α-tocopheroxyl radical recycling by ascorbate.
authors.affiliation: Department of Molecular Medicine, University of Padova and Istituto Nazionale Biostrutture Biosistemi, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Vanzani
authors.affiliation: Istituto Nazionale Biostrutture e Biosistemi, Italy.
authors.forename: Adelio
authors.initials: A
authors.lastname: Rigo
authors.affiliation: Department of Molecular Medicine, University of Padova and Istituto Nazionale Biostrutture Biosistemi, Italy.
authors.forename: Lucio
authors.initials: L
authors.lastname: Zennaro
authors.affiliation: Department of Molecular Medicine, University of Padova and Istituto Nazionale Biostrutture Biosistemi, Italy.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Di Paolo
authors.affiliation: Department of Physics, University of Trento and Istituto Nazionale Biostrutture e Biosistemi, Italy.
authors.forename: Marina
authors.initials: M
authors.lastname: Scarpa
authors.affiliation: Department of Molecular Medicine, University of Padova and Istituto Nazionale Biostrutture Biosistemi, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Rossetto
mesh_terms: D005609:Free Radicals / Q000737:chemistry; D006801:Humans; D008074:Lipoproteins / Q000097:blood / Q000737:chemistry*; D008823:Micelles; D024502:alpha-Tocopherol / Q000737:chemistry*
chemical_list: D005609:Free Radicals; D008074:Lipoproteins; D008823:Micelles; D024502:alpha-Tocopherol
keywords: Antioxidant; Ascorbate; Dismutation rate constant; Tocopherol; Tocopheryl quinone; Vitamin E