1-O-Alkylglycerol Ether Lipids in Two Holothurian Species: Cucumaria japonica and C. okhotensis

Abstract

Alkylglycerol ether lipids were investigated in two holothurian species, Cucumaria japonica and C. okhotensis. Species specific differences in the content of 1-O-alkylglycerol ether lipids were found. Some alkyl radicals of the 1-O-alkylglycerol ether lipid molecules contained branched hydrocarbon chains. The ratio between the content of linear and branched saturated 1-O-alkylglycerol ether lipids was 1.53 in C. okhotensis and 0.55 in C. japonica.

Unusual Ether Lipids and Branched Chain Fatty Acids in Sea Cucumber (Cucumaria frondosa) Viscera and Their Seasonal Variation

“…Analysis of the components of glyceryl ethers derived from both DAGE and MAGE revealed unique alkyl chain structures that were characteristically rich in 16:0 and 18:0 (Figure 2). Other studies have found a similar dominance of 16 and 18 carbon O-alkyl chains in DAGE and MAGE of C. japonica, C. okhotensis and Oneirophanta mutabilis [5,18]. This narrow range of alkyl structures indicates a high specificity for particular substrates in the pathways responsible for the biosynthesis of alkylglycerols [26].…”

“…The presence of ether lipids in C. frondosa viscera was expected as alkyl structures including saturated (branched and unbranched) and monounsaturated alkyl chains associated with an ether bond in glycerol ethers have been previously identified in Holothurians [ 5 , 6 , 18 ]. High levels of α-glyceryl ethers have been reported in lipid extracts of Stichopus japonicas (18%), C. fraudatrix (9.3%), and C. japonica and C. okhotensis (25–27%) [ 5 , 6 ].…”

“…The presence of ether lipids in C. frondosa viscera was expected as alkyl structures including saturated (branched and unbranched) and monounsaturated alkyl chains associated with an ether bond in glycerol ethers have been previously identified in Holothurians [ 5 , 6 , 18 ]. High levels of α-glyceryl ethers have been reported in lipid extracts of Stichopus japonicas (18%), C. fraudatrix (9.3%), and C. japonica and C. okhotensis (25–27%) [ 5 , 6 ]. The presence of DAGE ether lipids in other marine species including, for example, dogfish, shark, deep-sea squids, elasmobranch fish, oysters, sponges, snails and corals [ 7 , 8 , 19 , 20 , 21 , 22 , 23 , 24 ] suggests that they are ubiquitous in marine animals and therefore their presence in sea cucumber species such as C. frondosa is not surprising; however, total DAGE and MAGE detected here in winter was >55%, exceeding even that reported in some species of shark liver oil [ 25 ] and representing a valuable source of non-polar ether lipids.…”

“…This narrow range of alkyl structures indicates a high specificity for particular substrates in the pathways responsible for the biosynthesis of alkylglycerols [ 26 ]. Rybin et al [ 5 ] and Santos et al [ 18 ] had suggested that the specificity might be due to two acyl-CoA reductase isoenzymes (FAR1 and FAR2) [ 27 , 28 ]. Both reductase isoenzymes select fatty acyl-CoA of 16 and 18 carbon chains; FAR2 is specific for palmityl-and stearyl-CoA substrates, while FAR1 targets monounsaturated palmitoleyl- and oleyl-CoA and polyunsaturated linoleyl-CoA [ 29 ].…”

“…Freeze-dried powders of C. frondosa harvested off the coast of Newfoundland [ 4 ] were reported to contain up to nine lipid classes including hydrocarbons, steryl esters, ethyl ketones, triacylglycerols (TAG), free fatty acids (FFA), alcohols, sterols, and phospholipids (PL). However, other studies of related species in the Holothurian class of sea cucumber, including C. japonica , C. okhotensis , C. fraudatrix and Stichopus japonicas , have identified ether lipids, specifically 1- O -alkylglyceryl ethers [ 5 , 6 ]. Diacylglyceryl ethers (DAGE) and monoacylglyceryl ethers (MAGE) have been reported in several marine animals, such as in the livers of dogfish and shark [ 7 ] and deep-sea squids ( Berryteuthis magister ) [ 8 ].…”