Membrane plasmalogens

Plasma amine oxidase 886 Plasma antithrombin III 177 Plasma membrane 12, 379 Plasmalemma. See Plasma membrane Plasmalogens 383s, 384 Plasmids 5, 248249 ColEl 248 drug resistance 248 Plasmin 634 Plasminogen 634 Plasmodesmata 10... 

Gas Chromatographic Determination of the Fatty Acid Pattern of Red Cell Membrane Plasmalogens in Healthy Children... 

Ethanol and choline glycerolipids were isolated from calf brain and beef heart lipids by PTLC using silica gel H plates. Pure ethanol amine and choline plasmalogens were obtained with a yield of 80% [74]. Four phosphohpid components in the purple membrane (Bacteriorhodopsin) of Halobacterium halobium were isolated and identified by PTLC. Separated phosphohpids were add-hydrolyzed and further analyzed by GC. Silica gel G pates were used to fractionate alkylglycerol according to the number of carbon atoms in the aliphatic moiety [24]. Sterol esters, wax esters, free sterols, and polar lipids in dogskin hpids were separated by PTLC. The fatty acid composition of each group was determined by GC. 

Some animal tissues and some unicellular organisms are rich in ether lipids, in which one of the two acyl chains is attached to glycerol in ether, rather than ester, linkage. The ether-linked chain may be saturated, as in the alkyl ether lipids, or may contain a double bond between C-l and C-2, as in plasmalogens (Fig. 10-9). Vertebrate heart tissue is uniquely enriched in ether lipids about half of the heart phospholipids are plasmalogens. The membranes of halophilic bacteria, ciliated protists, and certain invertebrates also contain high proportions of... 

Most cells continually degrade and replace their membrane lipids. For each hydrolyzable bond in a glycerophospholipid, there is a specific hydrolytic enzyme in the lysosome (Fig. 10-15). Phospholipases of the A type remove one of the two fatty acids, producing a lysophospholipid. (These esterases do not attack the ether link of plasmalogens.) Lysophospholipases remove the remaining fatty acid. 

Inclusion of other molecules of irregular shape within membranes also lowers Tm. However, a molecule of cholesterol can pack into a bilayer with a cross-sectional area of 0.39 nm2, just equal to that of two hydrocarbon chains.49 It tends to harden membranes above Tm but increases mobility of hydrocarbon chains below Tm.97 -100 A complex of cholesterol and phosphatidylcholine may form a separate phase within the membrane.101102 The ether-linked plasmalogens may account for over 30% of the phosphoglycerides of the white matter of the brain and of heart and ether linked phospholipids are the major lipids of many anaerobic bacteria.103 Their Tm values are a few degrees higher than those of the corresponding acyl phospholipids.104... 

Plasmalogens protect biological structures against free radical attack (Maeba and Ueta, 2004 Engelmann, 2004) (Fig. 9.4). In neural membranes, transition metal... 

Farooqui A. A., Rapoport S. I., and Horrocks L. A. (1997). Membrane phospholipid alterations in Alzheimer disease deficiency of ethanolamine plasmalogens. Neurochem. Res. 22 523-527. 

Maeba R. and Ueta N. (2004). A novel antioxidant action of ethanolamine plasmalogens in lowering the oxidizability of membranes. Biochem. Soc. Trans. 32 141-143. 

Phospholipid molecules form the lipid bilayer of cell membranes (Appendix 3). Plasmalogens and sphingomyelins are particularly abundant in brain tissue. 

The complex lipids in milk fat are comprised of the phosphoglycerides, phosphatidyl choline, phosphatidyl serine, phosphatidyl ethanolamine, phosphatidylinositol and plasmalogens. Also, the non-glyceride phospholipid, sphingomyelin, occurs in important amounts (Jensen, 2002). Bitman and Wood (1990) described the distribution of phospholipid classes in bovine milk and their fatty acid composition. The phospholipids comprise about 1% and cholesterol 0.4—0.5% of the total milk fat. These occur almost completely in the milk fat globule membrane. 

Myelin is modified plasma membrane. Myelin of the PNS resembles that of the CNS with respect to lipid composition. There is an enrichment in such specialized lipids as cerebroside and ethanolamine plasmalogen, and the high content of cholesterol plays an important role in control of membrane fluidity. The protein composition of PNS myelin is, however, distinct from that of CNS myelin. A single protein, P0, accounts for half of all protein of PNS myelin. Of the other proteins present, most are expressed in the CNS as well as the PNS but in quantitatively different amounts. Prominent among these proteins are myelin basic proteins and myelin-associated glycoprotein. 

Cholesterol and phospholipids. Most lipids found in myelin are common to other cellular membranes. Cholesterol content is high and cholesterol esters are not present in normal myelin. Phospholipids are also common to other cellular membranes, except for the great quantity of ethanolamine phosphoglycerides in the plasmalogen form. The synthesis of plasmalogens is modified in Zellweger syndrome which is a peroxisomal syndrome that also increases VLCFA. This syndrome and other peroxisomal diseases may cause demyelination (Powers, 2005). 

Plasmalogens are monoacyl monoalk-l-enyl ether forms of phospholipids. The most common forms of plasmalogens are the choline, ethanolamine, and serine derivatives. They are present in most animal tissues, especially in the mammalian brain. Plasmalogens are stmctural components of membranes. It has been proposed that plasmalogens protect membranes against oxidative stress (9). 

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. 

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