LIPID CLASS DISTRIBUTION OF HIGHLY UNSATURATED LONG CHAIN FATTY ACIDS IN MARINE DINOFLAGELLATES

The very long chain highly unsaturated C 28 fatty acids, octacosaheptaenoic [28:7(n‐6)] and octacosaoctaenoic acid [28:8(n‐3)], were found to be associated with phospholipids, obtained by fractionation of total lipid extracts into distinct lipid classes, in 4 and 6, respectively, of 16 examined dinoflagellates. An interfraction comparison of fatty acids associated with phospholipids and glycolipids has also shown that the phospholipid fractions contained the majority (over 75% in 12 of 16 strains) of docosahexaenoic acid [22:6(n‐3)] and traces of tetracosanoic acid (24:0). By contrast, the highly unsaturated C 18 fatty acids octadecatetraenoic [18:4(n‐3)] and octadecapentaenoic acid [18:5(n‐3)] were primarily recovered from a chloroplast‐associated glycolipid fraction comprised of monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol. In 12 of 16 strains, an interfraction comparison showed that over 90% of 18:5(n‐3) was found to be associated with glycolipids. These findings indicate that the C 28 fatty acids are located and probably synthesized in the cytoplasm or in an organelle other than the chloroplast, possibly with 22:6(n‐3) and 24:0 as precursors, whereas the C 18 fatty acids 18:4(n‐3) and 18:5(n‐3) are glycolipid constituents apparently synthesized within the chloroplast. The function(s) of these C 28 fatty acids as components of phospholipids in cellular membranes is currently unknown.