ANTIOXIDANT EFFECT OF COENZYME-Q ON HYDROGEN PEROXIDE-ACTIVATED MYOGLOBIN

In recent years increased attention has been focused on the reduced fo rms of coenzyme Q as antioxidant compounds inhibiting lipid peroxidati on in model systems and in biological membranes, but in spite of exten sive experimental evidences the molecular mechanisms responsible for t he antioxidant activity of ubiquinones are still debated. Ferrylmyoglo bin and/or its free radical form are regarded as powerful oxidizing ag ents capable of promoting oxidation of essential cellular constituents , particularly cell membranes. Therefore, we investigated the effects of ubiquinol on the formation and survival of ferryl species of myoglo bin and on metmyoglobin itself. The addition of a threefold molar exce ss of hydrogen peroxide to a solution of metmyoglobin induces the rapi d formation of a compound with the spectral characteristics of ferrylm yoglobin. The reaction is complete within 4 min, producing up to 76% o f ferrylmyoglobin, which remains stable for at least 30 min. The addit ion of ubiquinol-1 to the same solution provokes a rapid and progressi ve reduction of ferrylmyoglobin to metmyoglobin and oxymyoglobin. Ubiq uinol-1, furthermore, is also capable of protecting metmyoglobin again st oxidation when added in the solution before hydrogen peroxide. Ubiq uinol-1, indeed, is effective at both limiting the maximal ferrylmyogl obin level attained (59% inhibition) and accomplishing complete remova l of the ferryl form (in about 15 min). The results demonstrate that u biquinol is capable of reducing both ferrylmyoglobin and metmyoglobin to oxymyoglobin, providing a novel antioxidant mechanism for coenzyme Q.