Tunneling effect in the regeneration reaction of vitamin E by ubiquinol

A kinetic study of the regeneration reaction of vitamin E by ubiquinol has been carried out by means of stopped-flow spectroscopy. A substantial deuterium kinetic-isotope effect on the second-order rate constant and a deviation from a linear relationship in the Arrhenius plot have been observed. These results suggest that the tunneling effect plays an important role in the prevention of lipid peroxidation by ubiquinol in various tissues and mitochondria.