Eicosapentaenoic acid reactions

Detailed accounts of the biosynthesis of the prostanoids have been pubUshed (14—17). Under normal circumstances arachidonic acid (AA) is the most abundant C-20 fatty acid m vivo (18—21) which accounts for the predominance of the prostanoids containing two double bonds eg, PGE2 (see Fig. 1). Prostanoids of the one and three series are biosynthesized from dihomo-S-linolenic and eicosapentaenoic acids, respectively. Concentrations ia human tissue of the one-series precursor, dihomo-S-linolenic acid, are about one-fourth those of AA (22) and the presence of PGE has been noted ia a variety of tissues (23). The biosynthesis of the two-series prostaglandins from AA is shown ia Eigure 1. These reactions make up a portion of what is known as the arachidonic acid cascade. Other Hpid products of the cascade iaclude the leukotrienes, lipoxins, and the hydroxyeicosatetraenoic acids (HETEs). Collectively, these substances are termed eicosanoids. 

The pathways of conversion of linoleic and a-linolenic fatty acids to their respective fatty acid end-products (arachidonic and eicosapentaenoic acid) are described in Figures 11.11 and 11.12. The initial reaction in these... 

It was necessary to add over 10% buffer for the transesteiification of phosphatidyl choline by native lipase (5). Hydrolysis occurred as a side reaction in the hydrophobic solvent-water system. Tlie transesterification of phosphatidyl choline and eicosapentaenoic acid (EPA) was carried out in water-saturated n-hexane using palmitic acid-modified lipase. Table II shows the transesterification of phosphatidyl choline and EPA. Modified lipase made it possible for the transesterification of phospholipids in organic solvents. 

Cw-polyenoic acids are present at low concentrations in milk fat, because of the biohydrogenation reactions that take place in the rumen. These acids are comprised almost exclusively of linoleic acid (9c, 12c-18 2), about 1.2 to 1.7% and a-linolenic acid (9c, 12c, 15c-18 3), about 0.9 to 1.2% (Table 1.2). These two fatty acids are essential fatty acids they cannot be synthesised within the body and must be supplied by the diet. In recent times, the usage of the term essential has been extended to include derivatives of these fatty acids, which are not synthesised in significant quantities (e.g., eicosapentaenoic acid, 20 5 and docosahexaenoic acid, 22 6). The proportion of a-linolenic acid appears to be affected by the cow s diet the concentration is higher in milk from pasture-fed cows than in milk from barn-fed cows (Hebeisen et al., 1993 Wolff et al., 1995). In the case of linoleic... 

Supercritical fluid carbon dioxide (SC-CO2) fractionation of fish oil ethyl esters (EE) was employed to prepare EE of two omega-3 fatty acids, all cis-5,8,11,14, 17-eicosapentaenoic acid (EPA) and all cis-4,7,10,13, 16,19-docosahexaenoic acid (DHA) in 90% purity and to separate the synthetic triacylglycerols (TG), trieicosapentaenoylglycerol (tri-EPA), and tridocosahexaenoyl-glycerol (tri-DHA) in > 92% purity from other reaction mixture components. In the synthesis, glycerine reacted with EE and sodium glyceroxide catalyst to form TG. 

Thromboxane synthetase has been solubilized and partially purified from human >53 gnd bovine blood platelets and from sheep and bovine lung. The enzyme activity also has been studied in platelet membranes by several workers.39-63 Recent studies indicate that the same enzyme catalyses the formation of TXA2 and hydroxyheptadecatrienoic acid (HHT) in a bimolecular reaction and that the formation of both products is inhibited in parallel.34,60,61 These studies also show that the formation of HHT does not involve TXA2 as an Intermediate and that TXA2 is converted exclusively into TXB2. PGH, the endoperoxlde from eicosapentaenoic acid (C2O 5 3,8,11,14,17) is converted into thromboxane A (TXA ) by platele... 

Fig. 1. The n-3/n-6 metabolic pathways. Precursors of the n-3 (18 3n-3, linolenic acid) and n-6 (18 2n-6, (/.-linoleic acid) are converted by a series of desaturation and (adding double bonds) and elongation (adding carbon atoms to the hydrocarbon backbone) reactions. Note that the same enzymes catalyze n-3 and n-6 desaturation and elongation reactions. Major metabolites are indicated. PUFAs with 20-carbon backbones (20 4n-6, arachidonic acid, and 20 5n-3, eicosapentaenoic acid) are precursors to the eicosanoids (prostaglandins, leukotrienes, thromboxanes). Docosahexaenoic acid (22 6n-3) is also indicated. Note that only a limited part of the metabolic pathway is shown in this figure.

Eicosanoids Hormone-like compounds, including prostaglandins, thromboxanes, lipoxins, and leukotrienes, which are involved in many important biological processes in the human body (i.e., central nervous funchon, regulation of blood pressure, regulation of other hormones, inhammatory reactions, and immune response). They are produced mainly through the metabohsm of arachidonic acid and eicosapentaenoic acid,although other fatty acids may also be similarly metabolized. 

SC-CO2 medium, there seemed to be no impairment by the adhesion. This should be owing to very strong permeability of the SC-CO2 allowing the dissolved substrate to contact snfficiently with the phospholipase Aj. Under the aforementioned optimum reaction condition, the obtained LPC derived from squid PC contained approximately 73% DHA and 18% eicosapentaenoic acid (EPA), as shown in Table 20.1, whereas the original substrate squid PC contained 45% DHA and 7% EPA. 

Han, JJ and Yamane, T (1999) Enhancement of both reaction yield and rate of synthesis of structured triacylglycerol containing eicosapentaenoic acid under vacuum with water activity control. Lipids, 34, 989-995. 

The fishy aroma of seafood is incorrectly attributed to trimethyl amine. Flavor formation in fresh and saltwater fish results from complex enzymatic, oxidative, and microbial reactions of n-3 polyunsaturated fatty acid precursors (e.g., eicosapentaenoic acid) (69,70). Hence, fish flavor is mostly composed of non-characterizing planty or melon-like aromas from lipid-derived unsaturated carbonyl compounds. Examples are (Z)-l,5-octadien-3-one ( geranium-like ) in boiled cod (71) and (7i,Z)-2,6-nonadienal ( cucumber-like ) in boiled trout (72). 

Jiittner, F. (2001) Liberation of 5,8,11,14,17-eicosapentaenoic acid and other polyimsaturated fatty acids from lipids as a grazer defense reaction in epilithic diatom biofilm. /. Phycol, 37, 744—755. 

Although these are termed essential fatty acids, they are, in fact, precursors for the major polyunsaturated fatty acids that have essential roles in the body but are present only in small amounts in the diet. Linoleic acid is converted, via elongation and desaturation reactions, to dihomo-y-linolenic (20 3n-6) and then to arachidonic (20 4n-6) acid. a-Linolenic is converted to eicosapentaenoic (20 5n-3) and then docosahexae-noic (22 6n-3). The pathways for formation of these latter fatty acids, from their dietary precursors, are presented in Figures 11.11 and 11.12. Full details of one pathway are provided, as an example, in Appendix 11.4. For comparison of the two pathways, they are presented side by side in Figure 11.13. 

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