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The effets of lipid peroxidation on the fluidity of the lipid bilayers of the human erythrocyte ghost and egg-lecthin phospholipid liposomes have been studied. For the measurements of the peroxidation extent and the fluidity of the membranes, the thiobarbituric acid-reactive substances and the fluorescene depolarization of 1,6-diphenyl-1,3,5-hexatrienen labelled into the membrane were employed, respectively. The lipid peroxidation was performed in hypoxanthine/xanthine oxidase/ferrous ion, and hydrogen peroxide/ferrous ion systems. The results of these experiments show that both of the xanthine oxidase and hydrogen peroxide systems effectively induced the lipid peroxidation of the ghosts. And the liposomal membranes, respectively. The lipid peroxidation decreased the fluidity of the membranes, especially at the very early stage of the peroxidation reaction. The decrease in the fluidity of membrane by the lipid peroxidation has been ascribed to the alteration of the polyunsaturated acyl chains of lipids and crosslinkings among the menbrane components. However, under drastic condition of lipid peroxidation, the fludity of the membrane rather increased possibly due to the deterioration of the membrane integrity by the peroxidation. Morhological change of the erythrocyte on peroxidation has also been observed.
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