Phosphatidylethanolamine, fatty acid composition

Jumpsen J, Lien EL, Goh YK, Clandinin MT. 1997. Small changes of dietary (n-6) and (n-3)/fatty acid content ration alter phosphatidylethanolamine and phosphatidylcholine fatty acid composition during development of neuronal and glial cells in rats. J Nutr 127 724-731. 

Table 3.7 The fatty acid composition of cholesteryl esters, phosphatidylcholine and phosphatidylethanolamine in the milks of some species... 

Some of the earlier data tabulated by Morrison (1970) on the fatty acid compositions of milk phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin are shown in Table 4.10. Included are analyses by Boatman et al. (1969) on phosphatidylethanolamine and phosphati-dylserine and by Bracco et al (1972) on phosphatidylinositol. The differences in composition between the samples of phosphatidylethanolamine and -serine can be attributed primarily to differences in metabolism. 

Hay and Morrison (1971) later presented additional data on the fatty acid composition and structure of milk phosphatidylethanolamine and -choline. Additionally, phytanic acid was found only in the 1-position of the two phospholipids. The steric hindrance presented by the four methyl branches apparently prevents acylation at the 2-position. The fairly even distribution of monoenoic acids between the two positions is altered when the trans isomers are considered, as a marked asymmetry appears with 18 1 between the 1- and 2-positions of phosphatidylethanolamine, but not of phosphatidylcholine. Biologically, the trans isomers are apparently handled the same as the equivalent saturates because the latter have almost the same distribution. There are no appreciable differences in distribution of cis or trans positional isomers between positions 1 and 2 in either phospholipid. Another structural asymmetry observed is where cis, cis nonconjugated 18 2s are located mostly in the 2-position in both phospholipids. It appears that one or more trans double bonds in the 18 2s hinders the acylation of these acids to the 2-position. 

Mutant T4 is considered to be defective in A9 desaturation [155]. Its mycelial fatty acids included 38% stearic acid (18 0) mainly as free fatty acids, the level being only 5% for the wild type. Since the fatty acid composition of phosphatidylethanolamine and phosphatidylcholine at sn-2 position included more than 75% of PUFA, the accumulation of free fatty acids was supposed to be due to the lack of PUFAs. 

Perhaps the major take-home message here is that the fatty acid composition of the inositol phospholipids is quite different from that found in phosphoglycerides such as phosphatidylcholine or phosphatidylethanolamine. The uniqueness rests on the narrow spectrum of fatty acid chain lengths present. 

Walnuts contain about 65% lipids, however, considerable differences exist among varieties (range 52-70%, w/w) (1,40). Walnuts also contain 15.8% protein, 13.7% carbohydrate, 4.1% water, and 1.8% ash (w/w) (1). The fatty acid composition of walnut oil is unique compared with other tree nut oils for two reasons walnut oil contains predominantly linoleic acid (49-63%) and a considerable amount of ot-linolenic acid (8-15.5%). Other fatty acids present include oleic acid (13.8-26.1%), palmitic acid (6.7-8.7%), and stearic acid (1.4—2.5%) (Table 5) (40). The tocopherol content of walnut oil varies among different cultivars and extraction procedures and ranges between 268 mg/kg and 436 mg/kg. The predominant tocol isomer is y-tocopherol (>90%), followed by a-tocopherol (6%), and then (3- and 8-tocopherols (41). Nonpolar lipids have been shown to constitute 96.9% of total lipids in walnut oil, whereas polar lipids account for 3.1%. The polar lipid fraction consisted of 73.4% sphingolipids (ceramides and galactosylcera-mides) and 26.6% phospholipids (predominantly phosphatidylethanolamine) (42). Walnut oil contains approximately 1.8g/kg phytosterols (1), primarily p-sitosterol (85%), followed by A-5-avenasterol (7.3%), campesterol (4.6%), and, finally, cholesterol (1.1%) (42). 

Almost all body cells contain phospholipids. The common animal phospholipids are made of sphingomyelin, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and other glycerol phospholipids of complex fatty acid composition. PC, formerly referred to as lecithin, PE, formerly referred to as cephalin, and PS are by far the most predominant phospholipids from most animal sources. As constituents of cell walls and active participants in metabolic processes, they appear to be essential to life (8). 

Phospholipids are a heterogeneous group of lipids. They mainly consist of phosphatidylcholine (ca. 67%), sphingomyelin (ca. 21 %o), lysolecithin (ca. 7%), and phosphatidylethanolamine (ca. 4%). Each of these constituents has a separate fatty-acid composition, (s. fig. 3.9)... 

Recent studies by Lin and co-workers [63] have shown that not only the fatty acid composition influences the kind and ratio of carbonyls formed during heating of lipids, but also the structure of the reaction medium. The type of self-assembly stmcture had a significant influence on reaction yields. Egg phosphatidylcholin, which forms a lamellar phase together with water, generated significantly more 41 than phosphatidylethanolamine which adopts a different nanostructure, namely a reversed hexagonal structure. 

The fatty acid composition of muscle lipids may show quantitative alterations in diseased muscle. Thus lecithin isolated from human dystrophic muscle had an increased amount of oleic but diminished linoleic acid (Tl). Changes have been recorded also in the fatty acid composition of lecithin from denervated muscle (PI). Recently it has been reported (K16) that the fatty acid pattern of muscle phosphatides from patients with the autosomal dominant form of myotonia congenita differed markedly from that of the autosomal recessive form and from the normal. Tani and his co-workers (F7) have made a detailed study of the phospholipids of normal and dystrophic mouse tissues. In normal mice phosphatidylcholine and phosphatidylethanolamine from skeletal and heart muscles had a very high content of 20-22-carbon polyunsaturated acids, in comparison with those for other tissues the most abundant was docosahexaenoic acid. In dystrophic mice there was a sharp decrease in the proportion of docosahexaenoic acid in the phosphoglycerides from skeletal and heart muscles, suggesting the likelihood of important alterations in muscle membranes. Somewhat similar studies have been reported by Owens (05), who also observed a fall in the proportion of docosahexaenoic acid, mainly in the phosphatidylcholine -j- choline plasmalogen fraction. 

Phospholipids are asymmetrically distributed in the lipid bilayer, with phosphatidylethanolamine predominating on the matrix side and phosphatidylcholine on the cytoplasmic side. Seventy-five percent of the cardiolipin is present on the matrix side of the membrane. The fatty acid composition of the phospholipids depends on the species, tissue, and diet. In all cases, sufficient unsaturated fatty acids are contained in the phospholipids to provide a highly fluid membrane at physiological temperatures. 

The fatty acid composition of phospholipids is not the same as that of TAG from the same material. The content of saturated fatty acids is usually higher, and the content of polyunsaturated fatty acids (PUFA) is often also high (Table 5.2), but differences exist even between phospholipid classes from the same material for example, in pig adipose tissue, phosphatidylethanolamines contain less saturated acids and more PUFA than phosphatidylcholines (Body, 1988) the content of eicosatetraenoic acid is par-... 

Most lecithins obtained during degumming of edible oils are not suitable for human consumption. Therefore, they are added back to the extracted oilseed meal and used as feed. Only soybean lecithin is snitable for human and industrial uses. Properties required for soybean lecithin are shown in Table 5.4 (adapted after Precise, 1985). The phospholipid fraction of soybean lecithin contains about 30 to 32% phosphatidylcholine, 22 to 28% phosphatidylethanolamine, 18 to 20% phosphatidyUnositol, 3 to 4% phosphatidylserine, and 20 to 29% other snbstances. The fatty acid composition of soybean lecithin is shown in Table 5.5. The technical soybean lecithin obtained by extraction with a hydrocarbon solvent is very different from the phospholipid fraction obtained by extraction with chloroform-methanol (after Folch). 

Influence of Dietary Conjugated Linoleic Acid (CLA 2.5%) on the Fatty Acid Composition of Total Lipids, Triacylglycerols, Phosphatidylcholine (PC), and Phosphatidylethanolamine (PE)... 

Selected Fatty Acid Composition of Liver Phosphatidylethanolamine (PE) and Phosphatidylcholine (PC) ... 

Chapman and co-workers (1966, 1967) studied the spectra of films of pure phospholipids, including phosphatidylcholine and phosphatidylethanolamine. Phospholipid spectra were extremely variable, changing markedly with temperature and method of sample preparation. In particular, the gel-to-fluid thermotropic transition causes the resultant vibrational bands to be smeared out and to be devoid of fine structure (Fig. 9.8). Wallach etal (1978) studied multibilayer films of pure phospholipids and phospholipid mixtures as a function of fatty acid composition, temperature and degree of hydration. Table 9.3 summarizes the main band frequencies observed in these studies. 

The lipids in lean beef consist of about 2 to 4% triacylglycerols and 0.8 to 1% phospholipids containing 44% polyunsaturated fatty acids, which are mainly subject to oxidation. Oxidation occurs initially in the phospholipids of ceUular and subcellular membranes, which are in close proximity to the heme catalysts of the mitochondria and microsomes. A typical fatty acid composition of beef membrane phospholipids includes 22% 18 2,2% 18 3,15% 20 4, less than 1% 20 5 and 2% 22 6. Phosphatidylethanolamine is the main phospholipid implicated in lipid oxidation of cooked meat. Chicken and turkey muscle are more susceptible to oxidation than beef, because of their higher polyunsaturated phospholipid fraction and relatively low levels of natural tocopherols. Red poultry muscles oxidize faster than white because of higher phospholipid and iron contents. 

Table 1- Fatty acid composition of phosphatidylcholine phosphatidylethanolamine (PE) from unadapted and PEG-adapted cells...

Phospholipase A2 Action. As in the case of phosphatidylcholine, the above-mentioned phospholipases will attack only the sn-3 form of naturally occurring (as well as synthetic) phosphatidylethanolamine. The products are, of course, lysophosphatidylethanolamine (1 -6>-acyl-2-lyso-.rn-glycero-3-phosphoethanolamine) and the fatty acids (liberated from the sn-2 position). The latter can be analyzed for composition and structure, as the methyl esters, by gas-liquid chromatography coupled with mass spectrometry. Usually these acyl groups are largely the unsaturated types. 

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