Biology Reference
In-Depth Information
CH2
O
CH2
CH2
alkyl ether
CH2
O
CH
CH
alkenyl ether
H
H C
O
CH
CH
R
1
O
R
2
H C
O
C
O
H C
H
O
P
O
ALCOHOL
-
O
PLASMALOGEN
FIGURE 5.4
Alkyl ether and alkenyl ether linkages and a plasmalogen. Plasmalogens have an ether link at the
sn
-1 position and an ester link at the
sn
-2 position.
those related to membranes. Vertebrate heart is particularly enriched in ether-linked lipids
where about half of the phosphatidylcholine is plasmalogen. Elevated levels of ether-linked
lipids in cancer tissues and their role as a platelet activating factor (important in molecular
signaling) have greatly stimulated interest in these compounds. Although their molecular
function remains unknown, it seems possible it is probably related in some way to its resis-
tance to hydrolysis or its ability to protect cells against the damaging effects of singlet oxygen.
Two main types of ether bonds exist in natural lipids, alkyl and alkenyl (vinyl) ethers
(
Figure 5.4
). The double bond adjacent to the oxygen atom in the alkenyl ether has a
cis
or
Z configuration.
B. PHOSPHOLIPIDS
The major type of animal membrane polar lipids is commonly referred to as phospholipids
(also referred to as glycerophospholipids, GP, in the Comprehensive Classification System of
Fahy et al., 2005,
[5]
). Phospholipids
[6
e
9]
are composed of 1 glycerol, 1 phosphate, 2 fatty
acids, and an alcohol. The molecule is constructed by removing 4 waters, creating 4 esters
(
Figure 5.5
). The phospholipid class name is derived from the alcohol. In animals there are
7 major classes of phospholipids (see
Figure 5.6
).
A phospholipid is amphipathic, having both a polar head group and two very hydro-
phobic, apolar acyl tails. Often a phospholipid is represented by a simple cartoon drawing
