Distribution of alkyl and alkenyl ether-linked phospholipids and platelet-activating factor-like lipid in various species of invertebrates.

The levels of alkenylacyl, alkylacyl and diacyl subclasses of choline glycerophospholipid (CGP) and ethanolamine glycerophospholipid (EGP) fractions in 28 species of various invertebrates were studied. We found that only small amounts of either 1-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl-GPC) or 1-alkenyl-2-acyl-sn-glycero-3-phosphoethanolamine (alkenylacyl-GPE) are present in most species of insects. On the other hand, almost all species examined in various phyla other than Arthropoda were shown to contain large amounts of both alkylacyl-GPC and alkenylacyl-GPE. The highest proportion of alkylacyl subclass in CGP was noted in sponge, Halichondria japonica (81.8% of CGP) and the highest proportion of alkenylacyl subclass in EGP was found in clam worm, Marphysa sanguinea (88.7% of EGP). We next surveyed the presence of platelet-activating factor (PAF)-like lipid in 45 species of invertebrates. PAF-like lipid was widely distributed among various lower animals. The highest value was obtained for sea cucumber, Stichopus japonicus, in which PAF-like lipid was present throughout the body. We also confirmed the presence of acetyltransferase activity in several lower animals. These results suggest that alkyl and alkenyl ether-linked phospholipids including PAF are physiologically important molecules particularly for invertebrates belonging to lower phyla.