Jc. Macpherson et al., PHOSPHOLIPID-COMPOSITION OF THE GRANULAR AMEBOCYTE FROM THE HORSESHOE-CRAB, LIMULUS-POLYPHEMUS, Lipids, 33(9), 1998, pp. 931-940
The phospholipid composition was determined for the amebocyte of the p
rimitive arthropod Limulus polyphemus. The total fatty acid compositio
n of the cells' lipids was analyzed by gas chromatography/mass spectro
metry (GC/MS) of fatty acid methyl esters (FAME). The FAME analysis re
vealed high levels of 20-carbon polyunsaturated fatty acids (PUFA), es
pecially arachidonic (20:4n-6) and eicosapentaenoic (20:5n-3) acids. A
lmost 20% of the total lipid profile was comprised of dimethyl acetals
of 16- to 20-carbon chain lengths, indicative of plasmalogens in the
phospholipid pool. Phospholipids, analyzed by high-pressure liquid chr
omatography, included phosphatidylethanolamine (PE), phosphatidylcholi
ne (PC), phosphatidylserine (PS), phosphatidylinositol (PI), sphingomy
elin (SPH), and cardiolipin (CL). PE and PC levels predominated at 42.
2 and 36.3%, respectively. Smaller amounts of PS (9.0%) and PI (6.2%)
were present, as well as low levels of SPH (4.6%), CL (1.6%), and trac
e amounts of lysophosphatidylcholine. The major phospholipid species,
PE, PC, PS and PI, were collected and their molecular species were exa
mined by electrospray-ionization mass spectrometry. The molecular spec
ies within the phospholipid classes reflected the high levels of PUFA
seen in the total lipid profile. PI was mainly composed of 18:0a/20:4.
Over half of the PS consisted of 18:0d18:1 and 18:0a/20:4. The major
PE species were 20:1p/20:5, 20:1p/20:4, 18:0p/20:5, and 18:0p/20:4. PC
had the largest distribution of molecular species, and its most abund
ant species were 16:0e/20:5, 16:0e/20:4, and 16:0p/20:4. The presence
of 16:0e/20:4 is the first documentation of a specific precursor to pl
atelet-activating factor in an invertebrate hemocyte. Note: at the sn-
1 position: [a = 1 = O-acyl, e = 1-O-alkylether, and p = 1-O-alk-1'-en
yl (plasmalogen)].