Lipids from nerve tissues of the horseshoe crab, Limulus polyphemus

Phospholipid composition of the granular amebocyte from the horseshoe crab, Limulus polyphemus

The phospholipid composition was determined for the amebocyte of the primitive arthropod Limulus polyphemus. The total fatty acid composition of the cells' lipids was analyzed by gas chromatography/mass spectrometry (GC/MS) of fatty acid methyl esters (FAME). The FAME analysis revealed high levels of 20-carbon polyunsaturated fatty acids (PUFA), especially arachidonic (20:4n-6) and eicosapentaenoic (20:5n-3) acids. Almost 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 chromatography, included phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI), sphingomyelin (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 trace amounts of lysophosphatidylcholine. The major phospholipid species, PE, PC, PS and PI, were collected and their molecular species were examined by electrospray-ionization mass spectrometry. The molecular species 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 18:0a/18:1 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 abundant 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 platelet-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'-enyl (plasmalogen)].

Studies on the methanolysis of small amounts of purified phospholipids for gas chromatographic analysis of fatty acid methyl esters

The methanolysis of small amounts of purified phosphoglycerides and sphingomyelin was studied and a quantitative comparison of five methods for the methanolysis of standard phosphoglycerides was made. These methods were based on methanolysis with boron trifluoride-methanol, methanolic sodium methoxide (at ambient temperature and with heating) and methanolic sulphuric acid. A further method was based on saponification with methanolic sodium hydroxide and subsequent esterification with boron trifluoride-methanol. Under the experimental conditions, only the sodium methoxide-catalysed method at ambient temperature gave complete methanolysis of phosphoglycerides. For methanolysis of sphingomyelin, boron trifluoride-methanol, methanolic sulphuric acid and methanolic hydrochloric acid were used. It was found that complete methanolysis of sphingomyelin takes 15 h at 90 degrees C. Based on these results, procedures for the methanolysis of phosphoglycerides and sphingomyelin separated by high-performance liquid chromatography are presented.