5-OCTADECENOIC ACID - EVIDENCE FOR A NOVEL TYPE OF FATTY-ACID MODIFICATION IN SCHISTOSOMES

The lipid metabolism of schistosomes is characterized by several intri guing adaptations to a parasitic way of living. The surface of the par asite consists of two closely apposed phospholipid bilayers, a structu re unique to blood flukes. Schistosomes do not synthesize fatty acids de novo, but are able to modify fatty acids, which they obtain from th e host, by chain elongation. Here we present evidence that schistosome s are capable of another type of fatty acid modification, resulting in the formation of 5-octadecenoic acid [C-18:1(5)]. This highly unusual fatty acid, which is absent in the blood of the host, was shown to be almost exclusively located in the outer membrane complex of the schis tosome. Within these membranes, it was almost exclusively present in o ne molecular phospholipid species, 1-palmitoyl-2,5-octadecenoyl phosph atidylcholine [C16:0-18:1(5)PtdCho]. Apart from dipalmitoyl phosphatid ylcholine, this was the most abundant phosphatidylcholine species in t he outer membrane complex. The specific synthesis by the schistosome o f C-18:1(5) and the highly specific localization of this fatty acid to the tegumental membranes suggest an important tegument-mediated role for this lipid.