Cis-trans isomerization of polyunsaturated fatty acid residues in phospholipids catalyzed by thiyl radicals

Phospholipids containing trans-unsaturated fatty acid residues are the majo r products of the thiyl radical attack on L-alpha -phosphatidylcholine from soybean lecithin in homogeneous solution or in liposomes (LUVET). Thiyl ra dicals act as the catalyst for the cis-trans isomerization, and the number of catalytic cycles depends on the reaction conditions. The presence of sim ilar to0.2 mM oxygen does not influence the reaction outcome but accelerate s the efficiency of cis-trans isomerization in homogeneous solution. Under these conditions, the PUFA peroxidation is found to be unimportant. A detai led study of the isomerization of methyl linoleate including product studie s indicates the formation of a small amount of conjugated dienes that act a s inhibitors. Indeed, all-trans-retinol substantially retarded the isomeriz ation process.