Role of Fatty Acids in Iodide-Complexing Lecithin

Abstract

The lecithin fraction of thyroid phospholipids was previously shown to be capable of complexing iodide, and effected active transfer of iodide from dilute solution in water through a semipermeable membrane into choloroform solution of lecithin in a model system. This effect was not found in other lecithins. The present paper elucidates further the composition of the fatty acids of lecithins that complex iodide. Nervonic acid (24:1) is found in appreciable amounts in iodide-complexing samples but not in lecithins without this function. Reattachment of nervonic acid into β-position of inactive thyro-lysolecithin restores its affinity toward iodide. If the β-palmitic acid in synthetic La- dipalmitoyl-lecithin is substituted by nervonic acid, this preparation becomes iodidecomplexing. The results suggest that α-acyl-β- nervonic-L-α-lecithin is responsible for most of the iodide-complexing function of the model system. The relevance of the finding to iodide transport in thyroid gland is discussed. (Endocrinology78: 453, 1966)