Erucic acid biosynthesis

As mentioned earlier, many seed oils produce a fatty acid that is different from the usual leaf fatty acids and which is characteristic of the plant family (Table II) (Smith, 1970 Hitchcock and Nichols, 1971). In general this makes a useful marker for seed oil development (Fig. 7). Caution is needed, since the characteristic fatty acid is not always exclusive to the oil. Appelqvist (1975) has demonstrated the presence of the monoenoic acid in the hypocotyls and testa ofB. napus, as well as in the cotyledons. It should be noted, however, that the structure of the major C22 monoenoic acid in the testa is not that of erucic acid (cis-13-docosenoic acid) but of an isomer, cis-15-docosenoic acid (Table VIII). Thus, if whole seeds are used in tracer studies of erucic acid biosynthesis or compartmentation, care must be taken in the interpretation of results if anjdysis is made only of the whole C22 monoene fraction (Appelqvist, 1975). Again it is emphasized that, although the subcellular compartmentation of erucic acid may not be exclusive to the major sites of oil storage, the compartmentation within lipid classes is absolutely exclusive to the triacyigiycerols as opposed to the polar lipids (Table III). 

Elongation by two carbon atoms occurs commonly in fatty acid biosynthesis. It is a variant of de novo chain-lengthening and occurs with acetyl or malonyl CoA or ACP derivatives. The substrate is any preformed saturated or unsaturated acid. For example, erucic (22 1) in high-emcic acid rapeseed oil and nervonic acid (24 1) in seed oil are formed from oleic acid by two and three elongations, respectively ... 

Lorenzo s Oil is a 4 1 mixture of the triglyerides of C22 l (erucic acid with cw-C13) and C18 l (oleic acid with cis-CQ). It was prepared by cosmetic chemist Don Suddaby of Croda International (who played himself). His most difficult task was to isolate large quantities of erucic acid from rapeseed oil. Lorenzo s Oil inhibits the biosynthesis of the detrimental saturated VLCFA but not the helpful unsaturated VLCFA. It did not reverse demyelination. 

III. BIOSYNTHESIS OF ERUCIC ACID IN DEVELOPING RAPESEED A. Early Experiments... 

It should be mentioned that the heavy investment in research on rapeseed not only yielded valuable information about the crop itself but also produced a body of scientific information which greatly helped in the understanding of fat metabolism and interspecies differences in metabolic pathways. The role of the chain shortening process and peroxisomal oxidation was made clearer by studies on docosenoic acid metabolism. Valuable information was obtained from experiments which dealt with the effects of erucic acid on adrenal gland activity and prostaglandin biosynthesis. Some excellent research was done also on the effect of erucic acid on cardiac mitochondrial respiratory activity. Moreover, some interesting theories were... 

The oil bodies of C. abyssinica synthesized fatty acids from [ Cjmalonyl-CoA and triacylglycerols from [ C]palmitoyl-CoA or [ C]glycerol-3-P (Gurr et al., 1974). Evidence that this was not due to contamination was, first, that the fat fraction synthesized a pattern of fatty acids (predominantly erucic acid) totally different from that of other subcellular fractions and, second, that of all the fractions tested only the fat fraction had an appreciable specific activity for triacylglycerol biosynthesis. In ultrastructural studies, no inclusions could be seen in Crambe oil bodies, and it was concluded that the enzymes were contained in a bounding membrane or in granular material that was always associated with the oil body fraction (Fig. 12). 

In Europe and the United States, a mixture of taUow and coconut oil is generally used. Palm oil and pahn kernel oil are used more frequently in the producing areas such as Africa and southeast Asia. Each fat molecule is made up of complex mixtures of natural fatty adds of different chain lengths from C4 (butyric acid) to C22 (erucic acid) (Table 25.1). The chains of fatty adds, which are derived from biosynthesis, are built from two carbon units, and cis double bonds are inserted by desaturase enzymes at specific positions resulting in even-chain-length fatty acids. The most common acids are Cjg and Cjg. 

There are many unsaturated fatty acids, characterized by having an alk-ene unit or diene or polyene units in the long carbon chain rather than the alkane chain found in 92-95. Common unsaturated fatty acids are palmitoleic acid (96 C16), oleic acid (97 C18), linolenic acid (98 C18), a-linolenic acid (99 C18), and y-linolenic acid (100 C18). Other examples include arachidonic acid (101 C20), erucic acid (102 C22— found in mustard seed), and nervonic acid (103 C24— important for the biosynthesis of nerve cell myelin). 

Since erucic acid (fZJ-13 22 1) is confined almost exclusively to the neutral lipid fraction in developing oilseeds [112], this fatty acid is an ideal marker for investigating enzymes involved in storage lipid biosynthesis. However, the mechanism for incorporation of (ZJ-13 22 1 into triacylglycerols is not fully understood, despite several studies aimed at elucidating the pathway in various oilseeds [113-119]. This is, in part, due to the fact that, traditionally, metabolism... 

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

Stumpf, P. K., and Pollard, M. R., 1983, Pathways of fatty acid biosynthesis in higher plants with particular reference to developing rapeseed, in "High and Low Erucic Acid Rapeseed Oil," J. K. G. Kramer, F. D. Sauer, and W. J. Plgden, ed.. Academic Press, New York. 

Bao, X., Pollard, M., Ohlrogge, J., 1998. The biosynthesis of erucic acid in developing embryos of Brassica rapa. Plant Physiol. 118, 183-190. 

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