Marine lipids
More variations in polyunsaturated fatty acid composition were noted
between lipid fractions. Poyunsaturated fatty acids of the (n-6) and
(n-3) series were particularly abundant. High levels of arachidonic acid
20:4 (n-6) and 24:3 (n-6) were found in neutral lipids (23% and 11%
respectively). Arachidonic acid was also present in the phospholipid fraction (6.4%). Three non-methylene-interrupted dienoic acids were characterized too: 7,11-18:2, 7,12-18:2 and 7,11-20:2.
Discussion
Saturated hexadecanoic (16:0) and octadecanoic (18:0) fatty acids represent 40-58% of total fatty acid composition. Those high percentages
are greater than those observed in a previous study of other gorgonians
of the family Plexauridae (in the genus Eunicea, 16:0 and 18:0 acids)
which accounted for 23-28% of total fatty composition (Carballeira et
al., 1997b). The lower level of monounsaturated fatty acids is quite
similar to that observed in previous works (Carballeira et al., 1997b).
The quite unusual 7-methyl-6-hexadecanoic acid (7-Me-Δ6-l6:l) has
already been identified in several marine invertebrates, such as sponges
or anemones. It could be of bacterial origin or a metabolite of endosymbiotic zooxanthella (Carballeira et al., 1996b).
In all lipid classes, (n-6) polyunsaturated fatty acids predominated, as
already shown for the genus Pseudopterogorgia (Carballeira et al., 1996a),
and for the genus Eunicea (Carballeira et al., 1997b). Polyunsaturated
24:6 (n-3) and EPA were not characterized in R. aggregata. The high percentages of 24:5 (n-6) were quite similar to those for rhe genus Eunicea
(Carballeira et al., 1997b). Arachidonic acid accounted for 23% of
neutral lipids. This polyenoic fatty acid possesses remarkable pharmacological properties in higher animals and is also an important prostaglandin precursor. It has already found to be a major fatty acid of the
gorgonian Plexaura homomalla, an other genus of the family Plexauridae
(Light, 1973) which also contained prostaglandin derivatives at high
levels. The non-methylene-interrupted dienoic acids were not previously described in the genus Ennicea.
Conclusion
This study and previous ones, indicate that the fatty acid composition
of R. aggregata is quite similar to that of the genus Eunicea (Carballeira
et al., 1997b), excepted for high 16:0 and 18:0 levels. R. aggregata,
unlike other marine organisms, rich in (n-6) polyunsaturated acids,
can also extend the fatty acid biosynthetic sequence to 24 carbons.
A new compound, 9-methyl-A6,9-heptadecadienoic acid (9-Me-Δ6,917:2) was thus identified. Work is in progress to elucidate the stereochemistry of double bonds by GC/FTIR. It is noteworthy that the 10methyl-Δ6,9-heptadecadienoic acid (10-Me-Δ6,9-17:2), an isomer of
this fatty acid, was previously identifiecl in Leptogorgia piccola (Mirallès
et al., 1995).
48
More variations in polyunsaturated fatty acid composition were noted
between lipid fractions. Poyunsaturated fatty acids of the (n-6) and
(n-3) series were particularly abundant. High levels of arachidonic acid
20:4 (n-6) and 24:3 (n-6) were found in neutral lipids (23% and 11%
respectively). Arachidonic acid was also present in the phospholipid fraction (6.4%). Three non-methylene-interrupted dienoic acids were characterized too: 7,11-18:2, 7,12-18:2 and 7,11-20:2.
Discussion
Saturated hexadecanoic (16:0) and octadecanoic (18:0) fatty acids represent 40-58% of total fatty acid composition. Those high percentages
are greater than those observed in a previous study of other gorgonians
of the family Plexauridae (in the genus Eunicea, 16:0 and 18:0 acids)
which accounted for 23-28% of total fatty composition (Carballeira et
al., 1997b). The lower level of monounsaturated fatty acids is quite
similar to that observed in previous works (Carballeira et al., 1997b).
The quite unusual 7-methyl-6-hexadecanoic acid (7-Me-Δ6-l6:l) has
already been identified in several marine invertebrates, such as sponges
or anemones. It could be of bacterial origin or a metabolite of endosymbiotic zooxanthella (Carballeira et al., 1996b).
In all lipid classes, (n-6) polyunsaturated fatty acids predominated, as
already shown for the genus Pseudopterogorgia (Carballeira et al., 1996a),
and for the genus Eunicea (Carballeira et al., 1997b). Polyunsaturated
24:6 (n-3) and EPA were not characterized in R. aggregata. The high percentages of 24:5 (n-6) were quite similar to those for rhe genus Eunicea
(Carballeira et al., 1997b). Arachidonic acid accounted for 23% of
neutral lipids. This polyenoic fatty acid possesses remarkable pharmacological properties in higher animals and is also an important prostaglandin precursor. It has already found to be a major fatty acid of the
gorgonian Plexaura homomalla, an other genus of the family Plexauridae
(Light, 1973) which also contained prostaglandin derivatives at high
levels. The non-methylene-interrupted dienoic acids were not previously described in the genus Ennicea.
Conclusion
This study and previous ones, indicate that the fatty acid composition
of R. aggregata is quite similar to that of the genus Eunicea (Carballeira
et al., 1997b), excepted for high 16:0 and 18:0 levels. R. aggregata,
unlike other marine organisms, rich in (n-6) polyunsaturated acids,
can also extend the fatty acid biosynthetic sequence to 24 carbons.
A new compound, 9-methyl-A6,9-heptadecadienoic acid (9-Me-Δ6,917:2) was thus identified. Work is in progress to elucidate the stereochemistry of double bonds by GC/FTIR. It is noteworthy that the 10methyl-Δ6,9-heptadecadienoic acid (10-Me-Δ6,9-17:2), an isomer of
this fatty acid, was previously identifiecl in Leptogorgia piccola (Mirallès
et al., 1995).
48