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 semi-permeable 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 [beta] -position of inactive thyrolysolecithin restores its affinity toward iodide. If the [beta] -palmitic acid in synthetic L-[alpha]-dipalmitoyl-leci-thin is substituted by nervonic acid, this preparation becomes iodide-complexing. The results suggest that [alpha] -acyl-[beta] -nervonic -L- [alpha] -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.