Sphingomyelin composition

Proulx [30] summarized the published lipid compositions of BBM isolated from epithelial cells from pig, rabbit, mouse and rat small intestines. Table 3.1 shows the lipid make-up for the rat, averaged from five reported studies [30], On a molar basis, cholesterol accounts for about 50% of the total lipid content (37% on a weight basis). Thus, the cholesterol content in BBM is higher than that found in kidney epithelial (MDCK) and brain endothelial cells (Table 3.1). Slightly different BBM lipid distribution was reported by Alcorn et al. [31] here, the outer (luminal) leaflet of the BBM was seen to be rich in sphingomyelin content, while the inner leaflet (cytosol) was rich in PE and PC. Apical (brush border) and basolateral lipids are different in epithelia. The basolateral membrane content (not reported by... 

The data in Table 4-1 indicate that myelin accounts for much of the total lipid of white matter, and that the lipid composition of gray matter is quite different from that of myelin. The composition of brain myelin from all mammalian species studied is very much the same. There are, however, some species differences for example, myelin of rat has less sphingomyelin than does that of bovine or human (Table 4-1). Although not shown in the table, there are also regional variations for example, myelin isolated from the spinal cord has a higher lipid-to-protein ratio than brain myelin from the same species. 

Peripheral and central nervous system myelin lipids are qualitatively similar. However, there are quantitative differences. PNS myelin has less cerebroside and sulfatide and considerably more sphingomyelin than CNS myelin. Of interest is the presence of the LM1 ganglioside, sialosyl-lactoneotetraosylceramide, as a characteristic component of myelin in the PNS of some species. These differences in lipid composition between CNS and PNS myelin are not, however, as dramatic as the differences in protein composition discussed below. 

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. 

Morrison (1970) presented earlier data on the fatty acid composition of these lipids. Morrison and Hay (1970) described the isolation and analyses of milk sphingomyelin, glucosylceramide, and lactosylcera-... 

Engelmann B., Streich S., SchonthierU. M., Richter W. O., and Duhm J. (1992). Changes of membrane phospholipid composition of human erythrocytes in hyperlipidemias. I. Increased phosphatidylcholine and reduced sphingomyelin in patients with elevated levels of triacylglycerol-rich lipoproteins. Biochim. Biophys. Acta Lipids Lipid Metab. 1165 32-37. 

Kreps (1981) and his associates (Akulin et al., 1969 Chebotareva, 1983), in their studies on Far East sockeye salmon, found that the fatty acid composition of lipids in the food influences not only that of the triacyl-glycerols of the fish but also the phospholipid fraction. This comprises, firstly, the phosphatidyl choline, phosphatidyl ethanolamine and phosphatidyl serine and, secondly, the sphingomyelin and cardiolipin. All tissues except nervous tissue were found by these workers to be strongly influenced by the composition of the food. However, the fatty acids of the brain have also been found to change according to the diet in European bass (Pagliarani et al., 1986), the proportions of phospholipid to non-phospholipid being unaffected. 

Deducing Lipid Structure from Composition Compositional analysis of a certain lipid shows that it has exactly one mole of fatty acid per mole of inorganic phosphate. Could this be a glyc-erophospholipid A ganglioside A sphingomyelin ... 

There are also differences in the composition of the phospholipids in human platelets. These cells contain a little over twice as much phosphatidylcholine as sphingomyelin. Another dramatic difference is noted in the ether phospholipid content in the human platelets, where there is approximately 37% vinyl ether-containing components in the ethanolamine fraction whereas there only are 10% or less in the other phosphoglyceride species. The vinyl ether linkage has not been detected in the sphingolipids of these cells. 

Sphingomyelin has a unique composition of fatty acids compared to the other phospholipids (Table 1.12) as the fatty acids are mainly long-chain saturated (i.e., 16 0, 22 0, 23 0 and 24 0). To illustrate the differences in fatty acid composition of sphingomyelin, the fatty acid analysis from another study is also listed. Furthermore, Bitman and Wood (1990) and Nyberg... 

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