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Arachidonic acid precursor

Cyclooxygenase (COX) activity is responsible for the formation of prostaglandins from their arachidonic acid precursor. Two COX isoforms have been identified, COX-1 and COX-2. While COX-1 is constitutively expressed in most tissues, COX-2 is typically only found after induction by proinflammatory stimuli. However, a constitutively expressed and highly regulated COX-2 is found in the kidney, both in the renal medulla and in the renal cortex. Renal cortical COX-2 is located in the area ofthe juxtaglomerular apparatus, and prostaglandins formed by COX-2 regulate the expression and secretion of renin in response to a reduction in NaCl concentration at the macula densa. [Pg.403]

Hydrolysis of phospholipids by PLDs—a family of enzymes of which none has yet been purified to homogeneity (but this is probably going to change in the near future)—produces phosphatidic acid and a non-phosphorylated polar head compound, such as choline or ethanolamine (Fig. 2.4 and 2.8). Needless to say, phosphatidic acid is biologically active (among other things, it stimulates protein phosphorylation), but we shall focus here only on its role as arachidonic acid precursor. Two enzymatic pathways are involved (Fig. 2.8). [Pg.34]

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. [Pg.151]

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... [Pg.240]

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. [Pg.816]

Eicosanoids and terpenoids are still other classes of lipids. Eicosanoids, of which prostaglandins are the most abundant kind, are derived biosynthetically from arachidonic acid, are found in all body tissues, and have a wide range of physiological activity. Terpenoids are often isolated from the essential oils of plants, have an immense diversity of structure, and are produced biosynthetically from the five-carbon precursor isopentenyl diphosphate (IPP). lsopentenyl diphosphate is itself biosynthesized from 3 equivalents of acetate in the mevalonate pathway. [Pg.1091]

Interest in the PGs has recently reverted to their precursor arachidonic acid (AA), which seems to be able to act intracellulary as a second messenger, and also extra-cellularly. In this latter mode it may play a part in LTP. It is known that AA produces a long-lasting enhancement of synaptic transmission in the hippocampus that resembles LTP and in fact activation of NMDA receptors leads to the release of AA by phospholipase A2 (see Dumuis et al. 1988) and inhibition of this enzyme prevents the induction of LTP. AA has also been shown to block the uptake of glutamate (see Williams and Bliss 1989) which would potentiate its effects on NMDA receptors. This would not only prolong LTP but also cause neurotoxicity. [Pg.281]

Microwave heating has also been employed for performing retro-Diels-Alder cycloaddition reactions, as exemplified in Scheme 6.94. In the context of preparing optically pure cross-conjugated cydopentadienones as precursors to arachidonic acid derivatives, Evans, Eddolls, and coworkers performed microwave-mediated Lewis acid-catalyzed retro-Diels-Alder reactions of suitable exo-cyclic enone building blocks [193, 194], The microwave-mediated transformations were performed in dichloromethane at 60-100 °C with 0.5 equivalents of methylaluminum dichloride as catalyst and 5 equivalents of maleic anhydride as cyclopentadiene trap. In most cases, the reaction was stopped after 30 min since continued irradiation eroded the product yields. The use of short bursts of microwave irradiation minimized doublebond isomerization. [Pg.172]

The title compounds LTB4, 21 (Z) and 22 (Z), have been synthesized23 by stereoselective reduction with deuterium gas of a 1 1 mixture of the suitable diacetylenic precursors 23 and 24 using Lindlar catalyst or palladium on barium sulphate catalyst (equation 10). Leukotriene B4, a 5-lipoxygenase metabolite of arachidonic acid, playing... [Pg.782]

Lipids have multiple roles in cells. Recent discoveries show that the same lipid may have both structural and regulatory roles in the cell. For example, while arachidonic acid (20 4co6) is a major constituent of brain inositides and PtdEtn, the free acid is also a precursor of a number of important bio messengers, the eicosanoids, such as prostaglandins, prostacyclins, leukotrienes and thromboxanes... [Pg.46]

Dietary polyunsaturated fatty acids (PUFAs), especially the n-3 series that are found in marine fish oils, modulate a variety of normal and disease processes, and consequently affect human health. PUFAs are classified based on the position of double bonds in their lipid structure and include the n-3 and n-6 series. Dietary n-3 PUFAs include a-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) whereas the most common n-6 PUFAs are linoleic acid, y-linolenic acid, and arachidonic acid (AA). AA is the primary precursor of eicosanoids, which includes the prostaglandins, leukotrienes, and thromboxanes. Collectively, these AA-derived mediators can exert profound effects on immune and inflammatory processes. Mammals can neither synthesize n-3 and n-6 PUFAs nor convert one variety to the other as they do not possess the appropriate enzymes. PUFAs are required for membrane formation and function... [Pg.192]

Arachidonic acid (C20 4 n-6) is the precursor for the synthesis of prostaglandin molecules (Section 4.4.4), which have a wide range of biochemical effects on for example, the perception of pain, inflammation, blood clotting and smooth muscle contraction. Docosahexaenoic acid (DHA, C22 6) and eicosapentaenoic acid (EPA, C20 5) are both n-3 long-chain polyunsaturated fatty acids (PUFA) which have been shown to have significantly beneficial effects on intellectual development and inflammatory conditions such as asthma and cardiovascular disease. [Pg.186]

Anandamide is believed to be synthesized from a phospholipid precursor, /V-arachidonoyl-phosphatidylethanolamine, catalysed by phospholipase D (Di Marzo et al. 1998). The other proposed route of synthesis is from condensation of arachidonic acid and ethanolamine, although this has yet to be demonstrated in living cells. 2-AG is formed in a calcium-dependent manner, and mediated by the enzymes phospholipase C and diacylglycerol lipase (Kondo et al. 1998 Stella et al. 1997). [Pg.412]

The omega (<0) numbering system is also used for unsaturated fatty acids. The co-family describes the position of the last double bond relative to the end of the chain. The omega designation identifies the major precursor fatty add, e.g., arachidonic add is formed from linoleic acid (co-6 family). Arachidonic acid is itself an important precursor for prostaglandins, thromboxanes, and leukotrienes. [Pg.207]

Fatty acids, such as linoleic, hnolenic, and arachidonic acids, contain two or more cis carbon-carbon double bonds and are referred to as polyunsaturated fatty acids. Several of these fatty acids, including linoleic and linolenic acids, are required nutrients for humans and must be part of a healthy diet. They are termed essential fatty acids, of which there are eight. These fatty acids cannot be synthesized by human beings but are essential to human health. Therefore, they must be consumed in adequate amounts in a healthy diet, specifically in the form of ingested plant-derived foods. A diet devoid of the essential fatty acids eventually results in a fatal condition characterized by inflammation of the skin (dermatitis), failure of wounds to heal, and poor growth. The essential fatty acids serve as precursors for complex molecules termed eicosanoids, to which we return below. [Pg.245]


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See also in sourсe #XX -- [ Pg.64 , Pg.69 ]




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