Phosphatide, phosphatidic acid, phosphatidylcholine, phosphatidylethanolamine

FIGURE 12.4 (A) Diagrammatic representation of the separation of major simple lipid classes on silica gel TLC — solvent system hexane diethylether formic acid (80 20 2) (CE = cholesteryl esters, WE = wax esters, HC = hydrocarbon, EEA = free fatty acids, TG = triacylglycerol, CHO = cholesterol, DG = diacylglycerol, PL = phospholipids and other complex lipids). (B) Diagrammatic representation of the separation of major phospholipids on silica gel TLC — solvent sytem chloroform methanol water (70 30 3) (PA = phosphatidic acid, PE = phosphatidylethanolamine, PS = phosphatidylserine, PC = phosphatidylcholine, SPM = sphingomyelin, LPC = Lysophosphatidylcholine). 

DMPC dimyristoyl phosphatidylcholine DOPC dioleoyl phosphatidylcholine DPPC dipalpalmitoylphosphatidylcholine DMPG dimyristoyl phosphatidylglycerol PAPC l-palmitoyl,2-arachidonoyl PC PDPC l-palmitoyl,2-docosahexaenoyl PC PA phosphatidic acid PE phosphatidylethanolamine PS phosphatidylserine... 

Abbreviations C = chloroform M = methanol DPG = diphosphatidylglycerol (cardio-lipin) PA = phosphatidic acid PE = phosphatidylethanolamine PS = phosphatidylserine PI = phosphatidylinositol PC = phosphatidylcholine. 

Figure 9.1 Structure of the most common phospholipids. PA = phosphatidic acid PE = phosphatidylethanolamine PC = phosphatidylcholine PS = phosphatidylserine PG = phos-phatidylglycerol PI = phosphatidylinositol.

Fig. 1. Chemical stmcture of phosphatidylcholine (PC) (1) and other related phosphohpids. R C O represents fatty acid residues. The choline fragment may be replaced by other moieties such as ethanolamine (2) to give phosphatidylethanolamine (PE), inositol (3) to give phosphatidylinositol (PI), serine (4), or glycerol (5). IfH replaces choline, the compound is phosphatidic acid (6). The corresponding lUPAC-lUB names ate (1), l,2-diacyl-t -glyceto(3)phosphocholine (2), l,2-diacyl-t -glyceto(3)phosphoethanolamine (3), 1,2-diacyl-t -glyceto(3)phosphoinositol (4), 1,2-diacyl-t -glyceto(3)phospho-L-serine and (5), l,2-diacyl-t -glyceto(3)phospho(3)-t -glycetol.

In addition to the triglycerides, the four oilseeds also contain phosphatides. For example, soybean oil containing 1.47% phosphatides consists of 48.9% phosphatidylcholine, 27.0% phosphatidylethanolamine, 21.9% phosphatidjlinositol and 2.2% phosphatidic acid (24). Total phosphatides of cottonseed and peanut kernels are estimated to be 1.5—1.9 and 0.8%, respectively (25). 

Figure 14-8. Phosphatidic acid and its derivatives. The 0 shown shaded in phosphatidic acid is substituted by the substituents shown to form in (A) 3-phosphatidylcholine, (B) 3-phosphatidylethanolamine,...

PC = phosphatidylcholine, PE = phosphatidylethanolamine, PS = phosphatidylserine, PI = phosphati-dylinositol, Sph = sphingomyelin, FA = fatty acid, PA = phosphatidic acid, LPI = lyso-PI, CL = car-diolipin, LPC = Iyso-PC, CHO = cholesterol, CE = cholesterol ester, TG = triglycerides. 

Glycerol utilization depends on the tissue. Adipose tissue can t use glycerol. Nitrogen-containing phospholipids are made from diglycerides, while other phospholipids are made from phosphatidic acid (PA). PI = phosphatidylinosi-tol PC = phosphatidylcholine PE = phosphatidylethanolamine PS = phos-phatidylserine. 

It can be seen from Figure 1 that the choline-containing phospholipids, phosphatidylcholine and sphingomyelin are localized predominantly in the outer monolayer of the plasma membrane. The aminophospholipids, conprising phosphatidylethanolamine and phosphatidylserine, by contrast, are enriched in the cytoplasmic leaflet of the membrane (Bretcher, 1972b Rothman and Lenard, 1977 Op den Kamp, 1979). The transmembrane distribution of the minor membrane lipid components has been determined by reaction with lipid-specific antibodies (Gascard et al, 1991) and lipid hydrolases (Biitikofer et al, 1990). Such studies have shown that phosphatidic acid, phosphatidylinositol and phosphatidylinositol-4,5-fc -phosphate all resemble phosphatidylethanolamine in that about 80% of the phospholipids are localized in the cytoplasmic leaflet of the membrane. 

Phosphatidic acid Phosphatidylethanolamine Phosphatidylcholine Occithin) Phosphatidylserine Phosphatidylinositol... 

Abbreviations. PC, phosphatidylcholine PE, phosphatidylethanolamine PI, phosphatidylinositol PA, phosphatidic acid. 

Lysophospholipids have been found in butter serum by Cho et al. (1977). They characterized the sn-1 and -2 lysophosphatidylcholines and phosphatidylethanolamines. It is not known if these compounds are products of degradation or remnants of biosynthesis. Cho et al. (1977) searched for, but did not find, another possible product of enzymatic degradation of milk, phosphatidic acid. Phosphatidic acid can be formed by the action of phospholipase D on phosphatidylcholine, for example, but this enzymatic activity was not detected. The compound is also an important intermediate in the biosynthesis of lipids, but the concentration in tissue is always very low. The amount is also low in milk. Cho et al. (1977) found 1.2 and 0.9 (percent of total lipid P) of the lyso compounds above. The quantities of the other phospholipids were phosphatidylethanolamine, 27.3 -choline, 29.1 -serine, 13.4 -inositol, 2.5 and sphingomyelin, 25.6. 

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).

Glycerophospholipids contain a glycerol skeleton to which two fatty acids are esterified saturated fatty acids occupy mostly sn-position 1, whereas unsaturated fatty acids are mainly present on sn-position 2. The third hydroxyl is linked to a phosphate group to which an organic base is mostly esterified (Fig. 1). The most important components of soybean lecithin are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Phosphatidic acid (PA) may become important due to the presence of phospholipase D this enzyme slowly converts PC into PA in vegetable lecithins. Phosphatidylserine (PS), phosphatidylglycerol (PG), and lyso-phosphatidylcholine (LPC) are known as minor components lysophospholipids contain only one acyl group per molecule. Besides, ether phospholipids occur in which one or both fatty acyl... 

Synthesis of most phospholipids starts from glycerol-3-phosphate, which is formed in one step from the central metabolic pathways, and acyl-CoA, which arises in one step from activation of a fatty acid. In two acylation steps the key compound phosphatidic acid is formed. This can be converted to many other lipid compounds as well as CDP-diacylglycerol, which is a key branchpoint intermediate that can be converted to other lipids. Distinct routes to phosphatidylethanolamine and phosphatidylcholine are found in prokaryotes and eukaryotes. The pathway found in eukaryotes starts with transport across the plasma membrane of ethanolamine and/or choline. The modified derivatives of these compounds are directly condensed with diacylglycerol to form the corresponding membrane lipids. Modification of the head-groups or tail-groups on preformed lipids is a common reaction. For example, the ethanolamine of the head-group in phosphatidylethanolamine can be replaced in one step by serine or modified in 3 steps to choline. 

Figure 8.1. The structure of some common phospholipids ( ) phosphatidylcholine, (b) phosphatidylethanolamine and (c) phosphatidic acid.

Fig. 20.3. Schematic representation of the main pathways in the lipid metabolism of parasitic flatworms. Boxed substrates are supplied by the host. Pathways present in mammalian systems but absent in parasitic flatworms are shown by open arrows. Abbreviations DAG, diacylglycerol CDP-DAG, cytidine diphosphodiacylglycerol Farnesyl PP, farnesyl pyrophosphate Geranyl PP, geranylpyrophosphate Geranylgeranyl PP, geranylgeranylpyrophosphate FlMG-CoA, hydroxymethylglutaryl-CoA TAG, triacylglycerol PA, phosphatidic acid PC, phosphatidylcholine PE, phosphatidylethanolamine PI, phosphatidylinositol PS, phosphatidylserine.

Our previous GC analyses of the transmethylated phosphatides from this material, commercial soybean "lecithin," have shown 54% linoleic acid and 5% linolenic acid. The material designated soybean "lecithin" of course contains not only phosphatidylcholine, but also substantial amounts of phosphatidylethanolamine, phos-phatidylinositol, and phosphatidic acid. Both of the latter would confer a substantial negative charge to the microdisperse particles. 

Fig. 1. Targeted lipidomics of anandamide metabolism. Postulated pathways of anandamide metabolism. Abbreviations PC, phosphatidylcholine PE, phosphatidylethanolamine NAT, JV-acyl transferase LPA, lysophosphatidic acid PA, phosphatidic acid NAPE, jV-acyl-phosphatidylethanolamine Lyso-NAPE, l-lyso,2-acyl-OT-glycero-3-phosphoethanolamine-JV-acyl ABHD-4, a//3 hydrolase-4 GP-anandamide, glycerophospho-anandamide PAEA, phospho-anandamide PLA, phospholipase A NAPE-PLD, NAPE phospholipase D PLC, phospholipase C FAAH, fatty acid amide hydrolase P, phosphatase COX, cyclooxygenase LOX, lipoxygenase CYP450, cytochrome P450 PDE, phosphodiesterase.

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