Marine lipids
Table 2 - Partial A5,9 demospongic acid composition of Cinachyrella aff.
schulzei (A), Trikentrion loeve (B), Gelliodes sp. cf. incrustans (C), Gelliodes sp.
(D), Pseudaxinella cf. lunaecharta (E) and Axinella sp. (F).
Fatty acids
A
B
C
D
E
F
5,9-26:2
2.0
1.4
7.1
7.7
20.3
___
6-Br-5,9-26:2
___
___
___
2.3
___
5.9
5,9,21-26:3
___
___
2.3
___
___
___
7-5,9-27:2
7.2
0.4
___
—
1.1
___
ai-5,9-27:2
1.5
0.7
___
___
0.6
2.9
5,9-27:2
2.3
0.4
1.0
6.1
1.1
—
i-5,9-28:2
3.6
0.2
___
—
—
___
5,9,21-28:3
5.8
0.7
___
___
0.6
___
5.9-28:2
2.9
2.5
___
1.1
0.2
___
5,9,23-30:3
0.9
14.8
___
___
0.9
___
5,9,25-30:3
___
2.1
___
___
___
—
Total number
15
15
4
10
13
6
Total %
30.5
24.7
10.5
22.3
30.4
28.1
Others ≥2%: 5,9-24:2; i- 5,9-25:2; 5,9,19-26:3; 5,9,23-28:3; 6-Br-5,9-27:2
14 C incorporation studies showed that these acids were synthesized via
homologation of the respective short-chain precursor myristic, palmitic
and palmitoleic acids, followed by desaturation. These precursors must
be provided by symbiotic microorganisms or diet. The desaturation
process was quite striking for 26:0, beginning at either the A5 or A9
position. Thus, the second double bond may be inserted on either side
of the existing one, unlike the formation of PUTAs in animals for which
the second double bond is only inserted between the first one and the
carboxyl group (Djerassi & Lam, 1991).
Our results show that the elongation process can occur in the (n-7)
even and odd monoenoic series and in the n-5 monoenoic series up to
30 carbon atoms, as shown above. The detection of even and odd A5
long-chain acids (Δ5-25:1 and A5-28.1) confirmed that A5 desaturation
could occur as a first desaturation step after chain elongation.
38