Occurrence of Hexacosapolyenoic Acids 26:7(n‐3), 26:6(n‐3), 26:6(n‐6) and 26:5(n‐3) in Deep‐Sea Brittle Stars from Near the Kuril Islands

Abstract

Significant amounts of polyunsaturated fatty acids (PUFA) with a chain length of 26 carbon atoms were detected in lipids of five deep water species of Ophiuroidea besides common fatty acids with chain lengths between 14 and 24. By means of hydrogenation, GC-MS of the methyl esters, and 4,4-dimethyloxazoline (DMOX) derivatives of these C26 acids were characterized as 5,8,11,14,17,20,23-hexacosaheptaenoic [26:7(n-3)]; 8,11,14,17,20,23-hexacosahexaenoic [26:6(n-3)]; 5,8,11,14,17,20- hexacosahexaenoic [26:6(n-6)]; and 11,14,17,20,23-hexacosapentaenoic [26:5(n-3)]. Concentrations of these acids varied from 0.3 to 4.5 mol% of the total FA. In all the samples investigated, the main component of C26PUFA was hexacosaheptaenoic acid 26:7(n-3). These C26PUFA are localized mainly in polar lipids. The presence of the possible biosynthesis precursors suggests that the C26PUFA are produced by the brittle stars, and are not accumulated from food sources. This finding can also explain the presence of small amounts of the 26:7(n-3) acid detected earlier in flesh lipids of the roughscale sole Clidoderma asperrimum, which feeds on deep water brittle stars. We suggest a possible scheme of the biosynthesis of C26 PUFA.

Fatty Acids of Echinoderms: Diversity, Current Applications and Future Opportunities

“…A number of very long-chain PUFAs, which may be of particular interest, have recently been identified in echinoderms from the abyssal and bathyal zones. Among the common FAs, of which 20:4n-6 and 20:5n-3 are the major ones, a series of homologues 21:4n-7, 22:4n-8, 23:4n-9, and 22:5n-5 has been detected in the sea star Eremicaster vicinus and the sea urchin Kamptosoma abyssale inhabiting the Kuril–Kamchatka Trench at depths of 5,210–6,183 m [ 43 ]. Besides these FAs, a new representative of the n-2 family, 22:6n-2, has been identified in this sea star and this sea urchin (1.6 and 0.3%, respectively) [ 43 ].…”

“…Among the common FAs, of which 20:4n-6 and 20:5n-3 are the major ones, a series of homologues 21:4n-7, 22:4n-8, 23:4n-9, and 22:5n-5 has been detected in the sea star Eremicaster vicinus and the sea urchin Kamptosoma abyssale inhabiting the Kuril–Kamchatka Trench at depths of 5,210–6,183 m [ 43 ]. Besides these FAs, a new representative of the n-2 family, 22:6n-2, has been identified in this sea star and this sea urchin (1.6 and 0.3%, respectively) [ 43 ]. Since these FAs were found in abyssal foraminifera, the authors suggest that the most plausible explanation for this composition is the presence of foraminifera in the diet of the species considered.…”

“…In addition to common FAs with chain lengths between C14 and C24, PUFAs with a chain length of C26 were detected in lipids of five brittle star species collected from the upper bathyal zones off the Kuril Islands, Northwest Pacific, at a depth 340–460 m [ 43 ]. These C26 acids, identified as 26:7n-3, 26:6n-3, 26:6n-6, and 26:5n-3, are localized mainly in polar lipids.…”

“…In addition to common FAs with chain lengths between C14 and C24, several unusual C26 PUFAs were also found in five deep-sea species of Ophiuroidea [ 43 ]. The long-chain FAs 26:7n-3, 26:6n-3, 26:6n-6, and 26:5n-3 were identified by hydrogenation, GC-MS of the methyl esters, and 4,4-dimethyloxazoline (DMOX) derivatives.…”

Fatty Acids of Abyssal Echinodermata, the Sea Star Eremicaster vicinus and the Sea Urchin Kamptosoma abyssale: A New Polyunsaturated Fatty Acid Detected, 22:6(n‐2)

“…Kharlamenko et al (, ) studied FA of foraminifera and megabenthic deposit‐feeders. It is worth mentioning that, in addition to widespread FA, a number of new and uncommon FA such as unspecified C26 polyunsaturated fatty acids (PUFA) were found in brittle stars (Drazen et al, ) and subsequently identified as a family of C26 PUFA with 5–7 double bonds (Svetashev and Kharlamenko, ). In foraminifera, 10 new FA were found, including PUFA 22:4(n‐8) and 23:4(n‐9) (Kharlamenko et al, ).…”