Biosynthesis of oleic acid

P.K. Raju and R. Reiser, The alternate route for the biosynthesis of oleic acid in the rat, Blochem.Blophys.Acta. 176 48-53 (1969). 

DuPont scientists were the first to clone FAD2 and FADS genes from the soybean (2). They also provided conclusive evidence for the mechanism of polyunsaturated fatty acid biosynthesis, when antisense or cosuppression of the FAD2 gene led to lower n-6 desaturase activity, and the accumulation of oleic acid in glycerolipids. This was demonstrated not only in soybeans, but also in other oilseed crops, such as canola and sunflower (Table 1). These transgenic events... 

In hepatocytes cultured in the presence of oleic acid, incorporation of pH]-water into secreted lipids and TG was lower than incorporation into synthesized lipids with the 3-thia fatty acids. ° A similar phenomenon was observed with pH]-glycerol as the radioactive precursor. This suggests that some of the hypotriglyceridemic effects of 3-thia fatty acids may arise from a reduction in biosynthesis and/or secretion of TG. 

In the biosynthesis of metabolically altered acetylenic compounds, various numbers of acetylenic bonds may be inserted and the chain shortened by a- or p-oxidation or both (Fig. 3.3). Triple bonds are usually introduced in a conjugated manner, although they may be separated by a methylene group from the initial double bond of oleic acid. Other compounds maintain the Z double bond and do not undergo an allylic rearrangement (Jente et al., 1988). 

While the transformation of oleic acid to dihydrosterculic acid and desaturation of the latter to sterculic acid were clearly established, the route of biosynthesis of the homologous cyclopropanoid and cyclopropenoid fatty acids could not be deduced from the results of experiments with seedlings and seed slices (Johnson et al., 1967 Hooper and Law, 1965). It appeared likely that dihydromalvalic acid was the immediate precursor of malvalic acid (Johnson et al., 1967), but it was not apparent whether dihydromalvalic acid was formed from a heptadecenoic acid or by a-oxidation of dihydrosterculic acid. The latter possibility appeared more likely in view of the labeling pattern of sterculic and malvalic acids isolated from H. syriacus seedlings that had been incubated with [l- C]acetate (Smith and Bu Lock, 1964). 

The results of labeling experiments in tissues and callus cultures of various Malva species indicate the sequence of reactions in Fig. 3 for the biosynthesis of fatty acids containing a three-membered carbocyclic ring (Yano et al., 1972a). Oleic acid is converted to dihydrosterculic acid, methionine, presumably as S-adenosylmethionine, being the methylene donor. The desat-... 

Figure 2.1. Biosynthetic relationships between unsaturated fatty acids, (a) Elongation and retroconversion of oleic acid (b) elongation and desaturation of linoleic acid (c) biosynthesis of prostaglandin E2 from arachidonic acid (d) elongation and desaturation of a-linolenic acid (e) elongation and desaturation of oleic acid.

Agrawal, V. P., Stumpf, P. K. (1985) Elongation systems involved in the biosynthesis of erucic acid from oleic acid in developing Brassica juncea seeds. 

Our data suggest an inhibition of fatty acid biosynthesis between the elongation step of palmitic acid and the desaturation of oleic acid yielding linolenic acid. 

Table 5.1). Some of these acetylenes have also been isolated from Solanaceous food plants such as tomatoes and aubergines, where they appear to be phytoalexins (see Section 5.2.2.1). The biosynthesis of polyacetylenes of the falcarinol-type follows the normal biosynthetic pathway for aliphatic Ciy-acetylenes (Bohlmann et al. 1973 Hansen and BoU 1986), with dehydrogenation of oleic acid leading to the Cig-acetylenes crep-enynic acid and dehydrocrepenynic acid, which is then transformed to C17-acetylenes by -oxidation (Figure 5.2). Further oxidation and dehydrogenation leads to acetylenes of the falcarinol-type as outlined in Figure 5.2. 

Lennartz, W. j., G. Scheverbrandt, and K. Bloch The biosynthesis of oleic and 10-methylstearic acids in Mycobacterium phlei. J. Biol. Chem. 237, 664 (1962). Lynen, F. Participation of acyl-CoA in carbon chain biosynthesis. J. Cellular Comp. Physiol. 54, 33 (1959). 

Biosynthesis of Unsaturated Fatty Acids. In the mammalian tissues, the forma-tion of monoene fatty acids is only possible. Oleic acid is derived from stearic acid, and palmitooleic acid, from palmitic acid. This synthesis is carried out in the endoplasmic reticulum of the liver cells via the monooxigenase oxidation chain. Any other unsaturated fatty acids are not produced in the human organism and must be supplied in vegetable food (plants are capable of generating polyene fatty acids). Polyene fatty acids are essential food factors for mammals. 

Macrolide aggregation pheromones produced by male cucujid beetles are derived from fatty acids. Feeding experiments with labeled oleic, linoleic, and palmitic acids indicate incorporation into the macrolide pheromone component [ 117 ]. The biosynthesis of another group of beetle pheromones, the lactones, involves fatty acid biosynthetic pathways. Japonilure and buibuilactone biosynthesized by the female scarab, Anomalajaponica, involves A9 desaturation of 16 and 18 carbon fatty acids to produce Z9-16 CoA and Z9-18 CoA,hydroxylation at carbon 8 followed by two rounds of limited chain shortening and cyclization to the lactone [118]. The hydroxylation step appears to be stereospecific [118]. 

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