De novo biosynthesis of linoleic acid in two non-insect invertebrates: The land slug and the garden snail

Abstract

Abstract. The de novo biosynthesis of linoleic acid [18:2(n-6)], a fatty acid considered to be essential for most animals, was demonstrated in the land snail, Bulimulis alternatus mariae, and the garden slug, Arion circumscriptus.Radiolabeled acetate injected into the animals was incorporated into both 18:2 and 20:2, as demonstrated by radio-high performance liquid chromatography (radio-HPLC) and radio-gas chromatography (radio-GC). GCmass spectrometry (GC-MS) of the methoxy derivatives of the 18:2 and 20:2 isolated from the snail showed that major isomers had the double bonds in the n-6,9 positions. Radio-gas-liquid chromatography (radio-GLC) of the ozonolysis products from the labeled dienoic fatty acid methyl esters showed that both ends of the molecules were labeled, confirming de novo synthesis. The production of linoleic acid by these animals suggests the capability to produce linoleic acid may be widespread in invertebrates. Key words. Linoleic acid biosynthesis; essential fatty acid; A 12 desaturase; Bulimulis alternatus mariae; Arion circumscriptus.Until recently, linoleic acid [ 18:2(n-6)] had been considered to be an essential fatty acid for all animals 3. The requirement for this fatty acid in the animal diet is due to the absence of a A i2 desaturase, the enzyme responsible for the insertion of the second double bond in oleic acid. Plants 4, some fungi 5 and protozoa 6 possess a A 12 desaturase and thus readily produce linoleic acid. Studies in the 1980s demonstrated that many, although by no means all, insect species also possess the ability to produce linoleic acid 7-~°, rendering them free from a dietary requirement of fatty acid. The A 12 desaturase was subsequently characterized in the house cricket 11 and the American cockroach I2. The observation that many insect species could produce linoleic acid suggested the possibility that other invertebrates might also have this capability. The results reported herein demonstrate that the land snail and the garden slug can biosynthesize linoleic acid and suggest that this biosynthetic capability is much more widespread among animals than previously thought. Materials and methodsLand snails, Bulimulis alternatus mariae, were obtained from Carolina Biological Supply Company, Burlington, NC. Garden slugs, Arion circumseriptus, were collected from gardens and marshy areas in Reno, NV. The animals were injected with 1 gCi each sodium [1-14C]acetate (50 ~tCi/mmol), and, after 24 h at room temperature, were killed by freezing at -20 °C. After thawing, lipid was extracted by homogenization in chloroform:methanol:water (1:2:1), and lipids were extracted by the method of Bligh and Dye? 3. Lipid classes were separated by thin layer chromatography (TLC) 7, and fatty acids from polar lipids and triacylglycerols were methylated as described 14. Labeled fatty acid methyl esters were analyzed by radio-HPLC on a Supelco LC-8 reverse-phase column with acetonitrile:water (75:25) as eluant. Radiolabeled fatty acid methyl esters were detected with a Radiomatic Instruments F...

Biosynthesis of essential fatty acids in Octopus vulgaris (Cuvier, 1797): Molecular cloning, functional characterisation and tissue distribution of a fatty acyl elongase

“…The FA biosynthesis pathways have been investigated in both terrestrial (van der Horst 1973(van der Horst , 1974Weinert et al 1993;Zhu et al 1994) and aquatic mollusc species (Chu and Greaves 1991;de Moreno et al 1976;Waldock and Holland 1984;Zhukova 1986Zhukova , 1991Zhukova , 2007Delaporte et al, 2005). It was shown that some molluscs have active FA elongation systems (Waldock and Holland, 1984;Zhukova, 1986;Delaporte et al, 2005).…”

Fatty acid characteristics in two symbiotic gastropods from a deep hydrothermal vent of the West Pacific

“…It is generally accepted that animals desaturate fatty acids using A9 desaturase, 1 6 0 and 18:O being at the base of desaturations and further elongations occurring via 16:107 and 18:lw9 synthesis (Gurr & James 1980). In contrast, plants are capable of A12 and A15 desaturations and thus constitute the main source of 0 3 and 0 6 PUFAs which are considered to be essential for animals (Gurr & James 1980, Sargent et al 1987Sargent et al , 1990 Weinert et al 1993). Although the enzyme responsible for this peculiar desaturation has not been investigated, Weinert et al (1993) supposed that these terrestrial gastropods use the same pathway as plants and some insects, based on a A12 desaturation of oleic acid (Cripps et al 1990, Borgeson et al 1991.…”

“…In contrast, plants are capable of A12 and A15 desaturations and thus constitute the main source of 0 3 and 0 6 PUFAs which are considered to be essential for animals (Gurr & James 1980, Sargent et al 1987Sargent et al , 1990 Weinert et al 1993). Although the enzyme responsible for this peculiar desaturation has not been investigated, Weinert et al (1993) supposed that these terrestrial gastropods use the same pathway as plants and some insects, based on a A12 desaturation of oleic acid (Cripps et al 1990, Borgeson et al 1991. Compared to other marine heterotrophic invertebrates, such as bivalve molluscs or crustaceans (Ackman et al 1971, Ackman & Hooper 1973, Dall et al 1991 or symbiotic mussels from the same hydrothermal site (Pranal 1995, Pranal et al in press), A. hessleri and Ifremeria nautilei display particularly high levels of linoleic acid in their tissues.…”

Phospholipase A2 in salivary glands isolated from tobacco hornworms, Manduca sexta

“…Exceptions include those species of insects (Blomquist et al, 1982;Cripps et al, 1986) and other invertebrates (Weinert et al, 1993) which are able to biosynthesize 18:2n-6 from 18:1n-9 by action of a Δ-12 desaturase (fatty acid notation described in Stanley-Samuelson et al, 1988;Stanley, 2004). PUFAs act in two areas of animal biology.…”