Antioxidant activity of carotenoids in multilamellar liposomes assayed by inhibition of formation of thiobarbituric acid-reactive substances was in the ranking:Mixtures of carotenoids were more effective than the single compounds. This synergistic effect was most pronounced when lycopene or lutein was present. The superior protection of mixtures may be related to specific positioning of different carotenoids in membranes.z 1998 Federation of European Biochemical Societies.

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A chemiluminescence (CL) flash kinetics on the addition of Fe2+ ions into oxidized low density lipoprotein (LDL) suspension has been studied. LDL oxidation was carried out at 37 degrees C without and in the presence of 5 or 50 microM of Cu2+. It has been found that under certain experimental conditions (the addition of excess iron ions, more than 1 mM) the amplitude of CL flash depended almost linearly (1) on the concentration of oxidized LDL and (2) on the extent of LDL oxidation measured as diene conjugates (DC) and 2-thiobarbituric acid-reactive substance (TBARS) accumulation. The corresponding correlation coefficients were: for TBARS -0.94 and for DC -0.97, in the case of LDL autooxidation; 0.72 and 0.98, in the case of copper-induced LDL oxidation. A sensitivity of the CL method was shown to be significantly enhanced (by more than two orders) in the presence of CL sensitizer--2,3,5,6-1H,4H-tetrahydro-9-(2'-benzoimidazolyl)-qui nolizin-(9,9a,1- gh)coumarin.