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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.

The generation of the superoxide ion in the oxidation of glutathione (GSH) by molecular oxygen has been demonstrated in the absence and in the presence of a catalytic amount of copper ion. An effort has been made to quantify the production of superoxide ion by an NMR method utilising Cu,Zn superoxide dismutase and to correlate it to the reaction mechanism. The oxidation process is first-order with respect to GSH and molecular oxygen, the ratio Δ[GSH]/Δ[O 2 ] being 4.0 ± 0.1. The rate of superoxide ion generation is independent of the GSH concentration and increases linearly with the O 2 concentration. The addition of Cu 2+ increases the rate of GSH oxidation and of O 2 consumption. Also in this case the oxidation process is first-order with respect to GSH and O 2 , while a saturation effect with respect to Cu 2+ is observed. A kinetic scheme involving the formation of a short-living charge-transfer complex between GSH and oxygen is proposed to explain the experimental data.