AUTOXIDATION AND ANTIOXIDANT ACTIVITY OF UBIQUINOL HOMOLOGS IN LARGE UNILAMELLAR VESICLES

The antioxidant activity of ubiquinol homologues with different side-c hain length such as ubiquinol-3 and ubiquinol-7 was compared with that of alpha-tocopherol when peroxidation was induced by the water-solubl e initiator 2,2'-azobis-(2 amidinopropane hydrochloride). In large uni lamellar vesicles containing equal amounts of alpha-tocopherol, ubiqui nol-3 and ubiquinol-7 the rates of inhibition were very similar but th e stoichiometric factor of quinols was similar to 1. To explain this l ow value, which is one-half of that found when the autoxidation was pe rformed in apolar solvents (Chem. Phys. Lipids (1992) 61, 121-130), th e oxidation of alpha-tocopherol and ubiquinol-3 initiated by the azoco mpound was studied both in methanol and in dimiristoyl-lecithin vesicl es. The results obtained show that the ubiquinol homologues undergo a radical chain reaction taking place at the polar interface and suggest that the average preferred location of both quinol headgroups is near to the outer surface of the bilayer.