phosphate moieties or glycan structures. The diacyl moieties are formed by fatty
acids, the composition of which in natural products is heterogeneous with respect
to their chain lengths (C 12 –C 22 ) and degrees of unsaturation. There are mostly sa-
turated fatty acyl moieties in thesn-1 position and unsaturated fatty acyl moieties in
thesn-2 position. The composition of the fatty acids depends on the source of the
phospholipids with marked preferences. Thus, fatty acids of phosphatidylcholine
(PC) from soybean contain 15.2 % palmitic, 7.4 % oleic, 6.4 % linolenic, 2.8 %
stearic, 67.7 % linoleic and 0.5 % other acids, whereas the fatty acid composition
of phosphatidylcholine (PC) from egg yolk consists of 38.5 % palmitic, 31.7 %
oleic, 11.8 % linoleic, 9.2 % stearic, 5,2 % docosahexaenoic, 1.7 % arachidonic,
and 1.8 % other acids (Gunstone, 1996). Thesn-2 carbon is a chiral center. The
structure of the naturally occurring phospholipids is equivalent to that ofL-glycer-
ol-3-phosphate. Glycerophospholipids with only one acyl moiety are called
lysophospholipids. In 1-lysophospholipids, the acyl moiety insn-1 position is lack-
ing, in 2-lysophospholipids thesn-2 position is free.
Other naturally occurring compounds belonging to the glycerophospholipids
(Figure 1) are ether glycerophospholipids such as plasmenylglycerophospholipids
(plasmalogens) and the platelet-activating factor (PAF). They are also derived
from the glycerophosphoric acid ester, but in comparison with the diacylglycero-
phospholipids they contain an alkenyl or an alkyl moiety instead of the acyl moiety
in thesn-1 position which is ether-linked to the glycerol backbone. Finally, the sphin-
gophospholipids are also based on phosphoric acid diesters with a long-chain amino
alcohol such as sphingosine orN-acylsphingosine (ceramide) as nonpolar compo-
220 12 Phospholipases Used in Lipid Transformations
Figure 1. Naturally occurring phospholipids.