cis-trans isomerization of monounsaturated fatty acid residues in phospholipids by thiyl radicals

Thiyl radicals reversibly attack the double bonds of methyl oleate and diol eoyl phosphatidyl choline (DOPC), thus producing methyl elaidate and the co rresponding phospholipids containing trans-fatty acid residues in high yiel d. These processes are radical chain reactions with relatively long chain l engths. The rate constant for the p-elimination of a thiyl radical from the adduct radical has been estimated to be 6 x 10(6) s(-1) at ambient tempera ture. The cis-trans isomerization of fatty acid residues in DOPC vesicles ( multilamellar vesicles and large unilamellar vesicles made by the extrusion technique) by a thiyl radical, generated from biologically relevant thiols , has also been studied in detail. The presence of 0.2 mM oxygen does not i nfluence the effectiveness of cis-trans isomerization in both homogeneous s olution and lipid vesicles. This process, which does not cause lipid degrad ation but permanent modification of the membrane constituents, ultimately i nfluences the barrier properties and functions of biological membranes.