Distribution of Very-Long-Chain Fatty Acids between Molecular Species of Different Phospholipid Classes of Two Soft Corals

Abstract

Fatty acids (FAs) of soft corals contain two very-long-chain tetracosapolyenoic acids (TPA, 24:5n-6 and 24:6n-3), which are chemotaxonomic markers of all species of the subclass Octocorallia. The distribution of TPA in molecular species of different phospholipid (PL) classes was investigated for the first time in the soft corals Sinularia macropodia and Capnella sp. From shallow waters of Vietnam. Phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI) were the major PL classes of S. macropodia and Capnella sp. More than thirty two molecular species of these four PL classes were determined by high resolution tandem mass spectrometry. 18:1e/20:4 PE, 18:0e/20:4 PC, 18:0e/24:5 PS, and 18:0/24:5 PI were the major molecular species of PL in both coral species. PE, PC, and PS mainly consisted of alkyl acyl and alkenyl acyl forms, but diacyl forms predominated in PI. TPA were the principal FAs in PS and PI, whereas 20:4n-6 was more abundant in PE and PC. Selective incorporation of TPA in the molecules of PS and PI are supposed to be a specific feature of the biosynthesis of PL in alcyonarians. To study the trophic and symbiotic relationships of soft corals, some molecular species of PS and PI with TPA may be applied as lipid molecular markers of coral polyps.