LIPOAMINO ACIDS WITH ETHER
LINKAGE
These lipids are glycerolipids and are mainly derived from homoserine,
they are characterics of algae. Some forms have an alanine moiety instead of
homoserine. As the polar head may be considered derived from betaine (N,N,N-trimethyl
glycine), these lipids are commonly named betain-type lipids.
The homoserine-derived lipids were first identified in a yellow-green algae, Ochromonas
danica (Chrysophyceae) where they account for more than 50% of total
lipids
(Brown AE et al., Biochemistry
1974, 13, 3476). It has been suggested that homoserine-derived lipids, which are formed
by an ether linkage between homoserine and a diacylglycerol molecule, are
widely distributed and even found in some higher plants (Rozentsvet
OA et al., Phytochemistry 2000, 54, 401). Furthermore, they were shown to be a
substitute for phospholipids in several plants (Brown AE et al., Biochemistry
1974, 13, 3476).
Acyl chains (R1, R2) are 18:0,
18:2(n-6), 18:3(n-6) or (n-3) in Dunaliella (Lynch DV et al., Plant Physiol
1984, 74, 198) and 20:5(n-3), in Chlorella minutissima (Haigh WG et
al., Biochim Biophys Acta 1996, 1299, 183) and mainly 18:1(n-9) in Acanthamoeba
(Furlong
ST et al., J Lipid Res 1986, 27, 1182).
This lipid was shown to be also present in a protozoa, Acanthamoeba, (Furlong
ST et al., J Lipid Res 1986, 27, 1182), a fungus (Epidermophyton floccosum)
and in several green algae (Volvox, Chlamydomonas, Ulva, Acetabularia,
Closterium) but is absent in others (Chlorella, Tetraselmis). It also
occurs in mushrooms (Hanus LO et al., J Food Lipids 2008, 15, 370), in vascular cryptogamic plants but not in seed plants (Sato N et al.,
Phytochemistry 1984, 23, 1625; Kunzler
K et al., Phytochemistry 1997, 46, 883).
As they contain a quaternary ammonium group, homoserine-derived lipids resemble
phosphatidylcholine in some respects, and a balance between their levels was
suggested (Eichenberger W, Plant Sci Lett 1982, 24, 91).
Alanine-derived lipids (diacylglyceryl
hydroxymethyltrimethyl-b-alanine)
was first identified in Ochromonas danica (Vogel G et al., Chem Phys
lipids 1990, 52, 99) and was shown to replace the homoserine-derived lipids in brown algae but are absent in the
greens (Eichenberger W, Plant Physiol Biochem 1993, 31, 213).
Another betain lipid, diacylglyceryl carboxyhydroxymethylcholine, was then
discovered in Pavlova lutheri (Haptophyceae) (Kato M et al.,
Phytochemistry 1994, 37, 279).
