- Ether lipid
Ether lipids are
lipids in which one or more of the carbon atoms on glycerolis bonded to an alkylchain via an etherlinkage, as opposed to the usual esterlinkage.
Ether lipids are called
plasmalogens (1-O-1'-alkenyl-2-acylglycerophospholipids) if these are glycerol-containing phospholipids with an unsaturated "O"-(1-alkenyl) ( vinyl ether) group at the first position on the glycerol chain. Platelet-activating factoris an ether lipid which has an acetylgroup instead of an acyl chainat the second position (SN-2).
The formation of the ether bond in mammals requires two enzymes, dihydoxyacetonephosphate acyltransferase (
DHAPAT) and alkyldihydroxyacetonephosphate synthase ( ADAPS), that reside in the peroxisome. cite journal |author=Hajra AK |title=Glycerolipid biosynthesis in peroxisomes (microbodies) |journal=Prog. Lipid Res. |volume=34 |issue=4 |pages=343–64 |year=1995 |pmid=8685243 |doi=] Accordingly, peroxisomal defects often lead to impairment of ether-lipid production.
Plasmalogens as well as some 1-O-alkyl lipids are ubiquitous and sometimes major parts of the
cell membranes in mammals and anaerobic bacteria. [cite journal |author=Paltauf F |title=Ether lipids in biomembranes |journal=Chem Phys Lipids |volume=74 |issue=2 |pages=101–39 |year=1994 |pmid=7859340 |doi=10.1016/0009-3084(94)90054-X] In archaea, ether lipids are the major polar lipids in the cell envelope and their abundance is one of the major characteristics that separate this group of prokaryotes from the bacteria. In these cells, diphytanylglycerolipids or bipolar macrocyclic tetraethers can form covalently linked 'bilayers'. [cite journal |author=Koga Y, Morii H |title=Recent advances in structural research on ether lipids from archaea including comparative and physiological aspects |url=http://www.jstage.jst.go.jp/article/bbb/69/11/69_2019/_article |journal=Biosci Biotechnol Biochem |volume=69 |issue=11 |pages=2019–34 |year=2005 |pmid=16306681 |doi=10.1271/bbb.69.2019]
Differences between the
catabolismof ether glycerophospholipids by specific phospholipases enzymes might be involved in the generation of lipid second messenger systems such as prostaglandins and arachidonic acidthat are important in signal transduction. [cite journal |author=Spector A, Yorek M |title=Membrane lipid composition and cellular function |url=http://www.jlr.org/cgi/reprint/26/9/1015 |journal=J Lipid Res |volume=26 |issue=9 |pages=1015–35 |year=1985 |pmid=3906008] Ether lipids can also act directly in cell signaling, as the platelet-activating factoris an ether lipid signaling molecule that is involved in leukocytefunction in the mammalian immune system. [cite journal |author=Demopoulos C, Pinckard R, Hanahan D |title=Platelet-activating factor. Evidence for 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine as the active component (a new class of lipid chemical mediators) |url=http://www.jbc.org/cgi/reprint/254/19/9355 |journal=J Biol Chem |volume=254 |issue=19 |pages=9355–8 |year=1979 |pmid=489536]
Another possible function of the plasmalogen ether lipids is as
antioxidants, as protective effects against oxidative stresshave been demonstrated in cell cultureand these lipids might therefore play a role in serum lipoproteinmetabolism. [cite journal |author=Brosche T, Platt D |title=The biological significance of plasmalogens in defense against oxidative damage |journal=Exp Gerontol |volume=33 |issue=5 |pages=363–9 |year=1998 |pmid=9762517 |doi=10.1016/S0531-5565(98)00014-X] This antioxidant activity comes from the enol ether double bond being targeted by a variety of reactive oxygen species. [cite journal |author=Engelmann B |title=Plasmalogens: targets for oxidants and major lipophilic antioxidants |journal=Biochem Soc Trans |volume=32 |issue=Pt 1 |pages=147–50 |year=2004 |pmid=14748736 |doi=10.1042/BST0320147]
ynthetic ether lipid analogs
Synthetic ether lipid analogs have cytostatic and cytotoxic properties, probably by disrupting membrane structure and acting as inhibitors of enzymes within signal transmission pathways, such as
protein kinase Cand phospholipase C.
A toxic ether lipid analogue
miltefosinehas recently been introduced as an oral treatment for the tropical disease leishmaniasis, which is caused by leishmania, a protozoalparasite with a particularly high ether lipid content in its membranes. [cite journal |author=Lux H, Heise N, Klenner T, Hart D, Opperdoes F |title=Ether--lipid (alkyl-phospholipid) metabolism and the mechanism of action of ether--lipid analogues in Leishmania |journal=Mol Biochem Parasitol |volume=111 |issue=1 |pages=1–14 |year=2000 |pmid=11087912 |doi=10.1016/S0166-6851(00)00278-4]
Wikimedia Foundation. 2010.