Chain elongation of fatty acids in the fish parasite Paratenuisentis ambiguus (Acanthocephala).

An active enzyme system for fatty acid chain elongation exists in Paratenuisentis ambiguus (Acanthocephala), which elongates [1-14C]palmitic acid consecutively to stearic and arachidic acid. Highest specific activity of radioactive elongation products was detected in phosphatidylethanolamines that seem to play an outstanding role as acceptors of saturated long-chain and very long-chain fatty acids. In contrast, incubation of P. ambiguus with monounsaturated [1-14C]oleic acid under similar conditions led to small proportions of labeled eicosenoic acid only. Analysis of the fatty acid pattern and stereospecific distribution at the glycerol backbone of phospholipids revealed that saturated acyl moieties with 18, 20, and 22 carbon atoms were esterified almost exclusively in the sn-1 position of phosphatidylethanolamines and -cholines, whereas polyunsaturated fatty acids were found predominantly in the sn-2 position of these phospholipids. From these results it may be concluded that the parasite channels saturated long-chain and very long-chain fatty acids predominantly to the sn-1 position of phospholipids in order to compensate for increasing membrane fluidity caused by the incorporation of high proportions of polyunsaturated fatty acids of aquatic feed.