PLASTOQUINOL AND ALPHA-TOCOPHEROL QUINOL ARE MORE ACTIVE THAN UBIQUINOL AND ALPHA-TOCOPHEROL IN INHIBITION OF LIPID-PEROXIDATION

Comparative studies of antioxidant activities of such natural prenylli pids as plastoquinol-9 (PQH(2)-9), alpha-tocopherol quinol (alpha-TQH( 2)), ubiquinol-10 (UQH(2)-10) and alpha-tocopherol (alpha-T) in egg yo lk lecithin liposomes have been performed. The investigated compounds showed oxidation under molecular oxygen in the order UQH(2)-10 > alpha -TQH(2) > PQH(2)-9 > > alpha-T. The corresponding second order rate co nstants have been determined in Tris buffer (pH = 6.5) and were 0.413, 0.268, 0.154 and 0.022 M-1/s, respectively. The inhibition order of F e2+-H2O2-induced lipid peroxidation, corrected for the amount of preny llipids oxidized during the initiation period, was alpha-TQH(2) > PQH( 2)-9 > alpha-T > UQH(2)-10 for 5 mol% of the antioxidants content in l iposomes. The radicals formed in the initiation phase of the reaction caused oxidation of 27.5-33% alpha-T, 40-64% UQH(2)-10, 42-85% PQH(2)- 9 and 43-80% alpha-TQH(2), depending on the antioxidant concentration in liposomes (5-1 mol%, respectively) which reflects approximately the ir reactivity against radicals derived from the Fenton reaction. The a ntioxidant activity of the investigated prenylquinols, in relation to the activity of alpha-T, in natural membranes is discussed. (C) 1997 E lsevier Science Ireland Ltd.