Abstract
The behavior of an organic hydroperoxide in the presence of lipid and/or α-tocopherol in model membranes has been studied using 14C-labeled cholesterol-5 α-hydroperoxide as the organic hydroperoxide.Cholesterol-5α-hydroperoxide in saturated phospholipid micelles is rapidly isomerized to cholesterol-7α-hydroperoxide. Such an isomerization is inhibited by α-tocopherol, but not by an α-tocopheryl analogue with a substituted OH group, present in the micelles, indicating the formation of hydrogen bonds between OH group in a-tocopherol and OOH group in the 5α-hydroperoxide.The double bonds in unsaturated phospholipid can also serve to form a hydrogen bond with OOH in the 5α-hydroperoxide moiety in the micelles.The resulting hydrogen-bonded complex could be decomposed by ironinduced lipid peroxidation, accompanied by isomerization of the 5α-hydroperoxide and the further degradation to the 7-ketocholesterol and 7α-hydroxycholesterol.When three components, such as unsaturated phospholipid, 5α-hydroperoxide and a-tocopherol, are present in the same micelles, they form hydrogen bonded complexes. Such complexes could be decomposed by iron in the ferrous state, yielding mainly 5α-hydroxycholesterol without significant change in the structure of α-tocopherol and peroxidative cleavage of unsaturated phospholipid.
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