Molecular Distinction of Phosphatidylcholine Synthesis between the CDP-Choline Pathway and Phosphatidylethanolamine Methylation Pathway

Department of Biochemistry, Wake Forest University, Winston-Salem, North Carolina, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 11/1999; 274(42):29683-8. DOI: 10.1074/jbc.274.42.29683
Source: PubMed


In addition to the CDP-choline pathway for phosphatidylcholine (PC) synthesis, the liver has a unique phosphatidylethanolamine (PE) methyltransferase activity for PC synthesis via three methylations of the ethanolamine moiety of PE. Previous studies indicate that the two pathways are functionally different and not interchangeable even though PC is the common product of both pathways. This study was designed to test the hypothesis that these two pathways produce different profiles of PC species. The PC species from these two pathways were labeled with specific stable isotope precursors, D9-choline and D4-ethanolamine, and analyzed by electrospray tandem mass spectrometry. Our studies revealed a profound distinction in PC profiles between the CDP-choline pathway and the PE methylation pathway. PC molecules produced from the CDP-choline pathway were mainly comprised of medium chain, saturated (e.g. 16:0/18:0) species. On the other hand, PC molecules from the PE methylation pathway were much more diverse and were comprised of significantly more long chain, polyunsaturated (e.g. 18:0/20:4) species. PC species from the methylation pathway contained a higher percentage of arachidonate and were more diverse than those from the CDP-choline pathway. This profound distinction of PC profiles may contribute to the different functions of these two pathways in the liver.

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Available from: Cynthia J Delong, Sep 23, 2015
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    • "We examined whether the polyunsaturated phospholipid species are indeed excluded from DRMs derived from biological membranes and we determined which specific phospholipid species are enriched in DRMs. We qualitatively and quantitatively analyzed the lipids that are present in the DRM fraction of biological membranes derived from three cell types with considerable differences in total lipid composition (Evans et al. 1980; Lynch et al. 1986; DeLong et al. 1999): Madin-Darby canine kidney (MDCK) cells, McArdle cells and porcine sperm. MDCK cells have a relative saturated lipid composition while McArdle cells are somewhat more unsaturated. "
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    ABSTRACT: Lipid rafts are micro-domains of ordered lipids (L o phase) in biological membranes. The L o phase of cellular membranes can be isolated from disordered lipids (L d phase) after treatment with 1 % Triton X-100 at 4 °C in which the L o phase forms the detergent-resistant membrane (DRM) fraction. The lipid composition of DRM derived from Madin-Darby canine kidney (MDCK) cells, McArdle cells and por-cine sperm is compared with that of the whole cell. Remarkably, the unsaturation and chain length degree of aliphatic chains attached to phospholipids is virtually the same between DRM and whole cells. Cholesterol and sphingomyelin were enriched in DRMs but to a cell-specific molar ratio. Sulfatides (sphingolipids from MDCK cells) were enriched in the DRM while a seminolipid (an alkylacylglycerolipid from sperm) was depleted from the DRM. Treatment with<5 mM methyl-ß-cy-clodextrin (MBCD) caused cholesterol removal from the DRM without affecting the composition and amount of the phospholipid while higher levels disrupted the DRM. The substantial amount of (poly)unsaturated phospholipids in DRMs as well as a low stoichiometric amount of cholesterol suggest that lipid rafts in biological membranes are more fluid and dynamic than previously anticipated. Using negative staining, ultrastructural features of DRM were monitored and in all three cell types the DRMs appeared as multi-lamellar vesicular structures with a similar morphology. The detergent resistance is a result of protein–cholesterol and sphingolipid interactions allowing a relatively passive attraction of phospholipids to maintain the L o phase. For this special issue, the relevance of our findings is discussed in a sperm physiological context.
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    • "Nevertheless, the last step catalysed by CPT can become rate limiting if the supply of diacylglycerol (DAG) is restricted (Gibellini and Smith 2010). Alternatively, PC can be synthesized by methylation of phosphatidylethanolamine (PE), catalysed by phosphatidylethanolamine N-methyltransferase (PEMT), which mainly operates in the liver and contributes to 30–40 % of PC in hepatocytes (DeLong et al. 1999; Reo et al. 2002; Sundler and Akesson 1975). Choline is an essential nutrient for animals, and its main fate is the biosynthesis of PC via the CDPcholine pathway (Li and Vance 2008). "
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    • "Alternatively , PC can be synthesized by methylation of PE, catalyzed by phosphatidylethanolamine N-methyltransferase (PEMT). This pathway mainly operates in the liver, and it could contribute to 30–40% of PC in hepatocytes (Sundler and Akesson, 1975; DeLong et al., 1999; Reo et al., 2002). PE is synthesized through the CDP-ethanolamine pathway, which is similar as the CDP-choline pathway. "

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