DT-DIAPHORASE MAINTAINS THE REDUCED-STATE OF UBIQUINONES IN LIPID VESICLES THEREBY PROMOTING THEIR ANTIOXIDANT FUNCTION

The activity of purified DT-diaphorase in the reduction of ubiquinone homologues of different side-chain length incorporated in uni- and mul tilamellar vesicles was determined. The direct relationship between th e reduced state of ubiquinones and the inhibition of lipid autoxidatio n induced by thermolabile azocompounds was also demonstrated. Results demonstrate that DT-diaphorase is able to generate and to maintain the reduced, antioxidant form of ubiquinones in both types of vesicles. F urthermore, the results reported herein show that, in the presence of nicotinamide adenine dinucleotide (NADH) and DT-diaphorase, ubiquinol- containing multilamellar vesicles exposed to a lipophilic azocompound did not undergo lipid peroxidation, whereas in vesicles lacking either NADH or DT-diaphorase, thiobarbituric acid reactive substances (TEARS ) formation occurred. It is suggested that DT-diaphorase may be respon sible for maintaining the reduced state of ubiquinones in various nonm itochondrial cellular membranes. Copyright (C) 1996 Elsevier Science I nc.