Linolenic acid synthesis

Fig. 1. Genes and associated alleles that regulate linolenic acid synthesis in soybean.

Sandri, J., and J. Viala, Direct Preparation of (Z,Z) 1,4-Dienic Units with a New C6 Homologating Agent Synthesis of a-Linolenic Acid, Synthesis, 271-275 (1995). 

In order to elucidate the mechanisms of alpha- linolenic acid synthesis in oil-seeds we have studied the biosynthesis and occurence of this acid in developing cotyledons of the high linolenic linseed (cv. Gleneig) and the linolenic acid deficient mutants, M1589, M1722 and Zero" derived from this variety. 

C. Willemot - Simultaneous inhibition of linolenic acid synthesis in winter wheat roots and frost hardening by BASF 13-338, a derivative of pyridazinone. Plant Physiol., 6Q, 1-4 (1977). 

Multiple Pathways of Linolenic Acid Synthesis Operate... 

MULTIPLE PATHWAYS OF LINOLENIC ACID SYNTHESIS OPERATE AND INTERACT IN LEAF TISSUE... 

Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty aeids include llnoleic and y-linolenic acids. These must be obtained by mammals in their diet (specifically from plant sources). Arachidonic acid, which is not found in plants, can only be synthesized by mammals from linoleic acid. At least one function of the essential fatty acids is to serve as a precursor for the synthesis of eicosanoids, such as... 

Figure 11.17 Supplementation of diet with y-linolenic acid to overcome a deficiency of A desaturase Supplementation of a diet with DOPA to overcome a deficiency of monooxygenase in Parkinson s disease. A desaturase is a rate-limiting enzyme in the synthesis of arachidonic acid. Supplementation of diet with y-linolenic acid bypasses this enzyme. Damage to neurones in the brain that use dopamine as a neurotransmitter causes a deficiency of rate-limiting a supplement - enzyme, tyrosine monooxygenase, which is bypassed by a supplement, DOPA (dihydroxyphenylalanine). DOPA (usually, described as L-DOPA) is considered by the medical profession as a drug but, in reality, it is a dietary supplement.

Two general classes of pheromone compound have been identified in moths, and these have some broad, although not uniform, associations with certain taxa. The polyene hydrocarbons and epoxides of various chain lengths are pheromones found in some subfamilies of the Geometridae and Noctuidae, and in the Arctiidae and Lymantridae (Millar, 2000). These compounds are probably derived from dietary Unoleic and linolenic acids. The other major class of pheromone compounds includes acetate, alcohols, and aldehydes, which are found in the Tortrici-dae, Pyralidae, Gelechiidae, Sessiidae, and Noctuidae. This class of compounds is derived from the insect s fatty acid synthesis pathway, with enzymatic modifications discussed above. Both classes of pheromone are broadly represented in the Noctuidae but are typically found in different subfamilies (Am et al., 1992,2003). 

Two fatty acids are dietary essentials in humans (see p. 361) linoleic acid, which is the precursor of arachidonic acid, the sub strate for prostaglandin synthesis (see p. 211), and linolenic acid, the precursor of other co-3 fatty acids important for growth and development. [Note A deficiency of linolenic acid results in decreased vision and altered learning behaviors.] Arachidonic add becomes essential if linoleic acid is deficient in the diet. 

Figure 21-3 Major pathways of synthesis of fatty acids and glycerolipids in the green plant Arabidopsis. The major site of fatty acid synthesis is chloroplasts. Most is exported to the cytosol as oleic acid (18 1). After conversion to its coenzyme A derivative it is converted to phosphatidic acid (PA), diacylglycerol (DAG), and the phospholipids phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). Desaturation also occurs, and some linoleic and linolenic acids are returned to the chloroplasts. See text also. From Sommerville and Browse.106 See also Figs. 21-4 and 21-5. Other abbreviations monogalactosyldiacylglycerol (MGD), digalactosyldiacylglycerol (DGD), sulfolipid (SL), glycerol 3-phosphate (G3P), lysophosphatidic acid (LPA), acyl carrier protein (ACP), cytidine diphosphate-DAG (CDP-DAG).

Fell et al. presented a micellar two-phase system in which fatty acid esters can be hydroformylated [30]. Short fatty acids react in a mixture of water and the substrate without adding any surfactants. The rhodium/NaTPPTS catalyst system was able to conduct the reaction of methyl 10-undecenoate at 100°C with 30-bar synthesis gas pressure with a conversion of 99% without any surfactant. The reaction of linolenic acid ester was hindered by phase transfer problems which could be overcome by employing surfactants. The addition decreased the reaction time, so the same rhodium catalyst could achieve a conversion for linolenic methyl ester of 100%. The authors... 

Saturated fatty acids or unsaturated fatty acids, such as oleic acid (18 1, n-9), can be synthesized by normal mammalian cells that posses elongation and desaturation enzymes (Rosenthal, 1987). However, the polyunsaturated fatty acids of the n-3 and n-6 group, such as linoleic acid (18 2, n-6) or linolenic acid (18 3, n-3), are essential nutrients for animals because they are precursors for the synthesis of eicosanoid hormones such as prostaglandins (Needleman et al., 1986). 

Figure 3.2. Pathways for ruminal and endogenous synthesis of rumenic acid (cis-9, trans-11 CLA) in the lactating dairy cow. Pathways for biohydrogenation of linoleic and linolenic acids yielding vaccenic acid trans-11 18 1) are shown in the rumen box and endogenous synthesis by A9-desaturase is shown in the mammary gland box. Adapted from Bauman et at. (2003).

Mammals can insert a cts-alkene into the chain, providing that it is no further away from the carbonyl group than C9. We cannot synthesize linoleic or linolenic acids (see chart a few pages back) directly as they have alkenes at Cl 2 and Cl 5. These acids must be present in our diet. And why are we so keen to have them They are needed for the synthesis of arachidonic acid, a C20 tetraenoic acid that is the precursor for some very interesting and important compounds. Here is the biosynthesis of arachidonic acid. 

Chemical synthesis of the metabolites on the linolenic acid cascade Biosynthesis and Metabolism Biosynthetic pathway in plants... 

JAs are derived from linolenic acid via an octadecanoid pathway consisting of several enzymatic steps (Figure 36). Multiple compartments in plant cells participate in JA synthesis. The early steps of this pathway occur in chloroplasts, where linolenic acid is converted to OPDA by means of the three enzymes lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC).867-869 Linolenic acid is oxygenated by 13-LOX producing a peroxidized fatty acid 13-hydroperoxylinolenic acid. The product is subsequently metabolized by AOS to an unstable compound allene oxide. Allene oxide is sequentially converted by AOC to produce OPDA. An alternative pathway from another trienoic fatty acid, hexadecatrienoic acid (16 3), is present in chloroplasts.870 In this pathway, dinor OPDA is produced instead of OPDA. OPDA and dinor OPDA are transported into the peroxisome. An ABC transporter involved in this transport was identified in... 

Figure 12-6 Eicosapentaenoic acid synthesis pathway from alpha-linolenic acid. Note that the enzymes necessary to the process are delta-6-desaturase and delta-5-desaturase. (From http //www.asthmaworld.org/OMEGA3.htm)...

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