Plasmalogens

Plasmalogens are phosphatidyl derivatives in which the fatty acid in the a position has been replaced by an unsaturated ether (10.50a). They are found in brain and nervous tissue. 

Infrared spectroscopy has been used extensively (Bergstrom et al., 1963) in establishing the structures of prostaglandins. Ram well et al. (1968) have presented a very interesting review on the prostaglandins including nomenclature, identification, biosynthesis, metabolism, methods for their analysis, and physical data. 

These compounds are, respectively 1 la,15(S)-dihydroxy-9-oxo-13-frans-prostenoic acid 15(S)-hydroxy-9-oxo-10,13-trans-prostadienoicacid 15(S)-hydroxy-9-oxo-8(12), 13-trans-prostadienoic acid 9a,lla,15(S)-trihydroxy-13-trans-prostenoic acid 9/S, lla,15(S)-trihydroxy-5-c/s,13-trans-prostadienoic acid and, 1 la,15(S)-dihydroxy-9-oxo-5-cIS,13- rans-prostadienoic acid. NMR and optical rotatory dispersion spectra have been determined for several of these compounds, and ultraviolet data have been given (Ramwell et al., 1968). 

The purpose of this chapter is to discuss the metabolism and roles of ether glycerophospholipids in manunalian tissues. 

The biosynthesis of plasmalogens has been elegantly reviewed by several investigators (Paltauf, 1994 Lee, 1998 Nagan and Zoeller, 2001 Murphy, 2001). Briefly, the first three enzymes of plasmalogen biosynthesis (dihydroxyacetone phosphate acyltransferase, alkyldihydroxyacetone phosphate synthase, and acyl/alkyl dihydroxyacetone reductase) are located in peroxisomes. The other enzymes, namely l-alkyl- n-GroP acyltransferase, l-alkyl-2-acyl-5n-GroP phosphohydrolase, and l-alkyl-2-acyl-jn-Gro  

CDP-choline (CDP-ethanolamine) choline (ethanolamine) phosphottansferase, are localized in the endoplasmic reticulum. The acylation of dihydroxyacetone phosphate (DHAP) by acyl-coenzyme A (acyl-CoA) is catalysed by dihydroxyacetone phosphate acyltransferase with formation of 

1-0-Alkyl-2-acyl-sr -glycerol + CDP-Ethanolamine l-0-Alkyl-2-acyl-sr -glycero-3-phosphoethanolamine Ethanolamine plasmalogen 

Acyl-DHAP + CoA 1-0-Alkyl-DHAP + RCOOH 1-0-Alkyl-sn-glycero-3-phosphate + NAD 1-0-Alkyl-2-acyl-SA7-glycero-3-phosphate + CoA 

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Plasmalogens are ether glycerophospholipids in which the alkyl moiety is d5-a,/3-unsaturated (Figure 8.10). Common plasmalogen head groups include choline, ethanolamine, and serine. These lipids are referred to as phosphati-dal choline, phosphatidal ethanolamine, and phosphatidal serine. 

The etlranolamine plasmalogens have ethanolamine in place of choline. 

What products would you obtain from hydrolysis of a plasmalogen (Problem 27.16) with aqueous NaOH With H36+ ... 

These compounds constimte as much as 10% of the phospholipids of brain and muscle. StmcmraUy, the plasmalogens resemble phosphatidylethanolamine but possess an ether link on the sn- carbon instead of the ester link found in acylglycerols. Typically, the alkyl radical is an unsamrated alcohol (Figure 14-10). In some instances, choline, serine, or inositol may be sub-stimted for ethanolamine. 

Figure 24-4. Biosynthesis of ether lipids, including plasmalogens, and platelet-activating factor (PAF). In the de novo pathway for PAF synthesis, acetyl-CoA is incorporated at stage, avoiding the last two steps in the pathway shown here.

In multiple sclerosis, which is a demyelinating disease, there is loss of both phospholipids (particularly ethanolamine plasmalogen) and of sphingolipids from white matter. Thus, the lipid composition of white matter resembles that of gray matter. The cerebrospinal fluid shows raised phospholipid levels. 

Plasmalogens and platelet-activating factor (PAF) are ether phospholipids formed from dihydroxyacetone phosphate. 

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. 

PLANCK EUNCTION GIBBS FREE ENERGY MASSIEU FUNCTION PLANCK S CONSTANT PLASMALOGEN SYNTHASE PLASMANYLETHANOLAMINE A -DESA-TURASE PLASMIN... 

The analysis of essential fatty acids involves hydrolysis of the ester bonds and subsequent formation of the fatty acid methyl esters, which can be separated by gas chromatography (GC) [10]. By accident, the plasmalogens are hydrolysed in the same reaction and the methylation reaction transforms them into dimethylacetals, which appear in the GC run of the fatty acid methyl esters [4]. 

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