AN UNUSUAL POLAR LIPID FROM THE CELL-MEMBRANE OF MYCOPLASMA-FERMENTANS

The major unidentified polar lipid (compound X), recently demonstrated in the cell membrane of Mycoplasma fermentans,was purified by prepara tive silicic acid column chromatography. Chemical analyses of acid-hyd rolyzed compound X revealed that, in addition to fatty acids, it conta ins glycerol, choline and phosphate in a molar ratio of approximately 1:1:2, and an amino acid that has a retention time similar to that of homoserine. The methylated fatty acid fraction of compound X was subje cted to gas-liquid chromatography and revealed methyl palmitate and me thyl stearate in a 4.6:1 molar ratio. The structure of compound X was further analyzed by combining mass spectrometry, P-31-NMR and H-1-NMR. The positive and negative fast atom bombardment spectra showed a majo r component of M(r) 1048 and a minor component of M(r) 1076. Two diffe rent phosphate groups were identified in each of the components by P-3 1-NMR. Fast atom bombardment, tandem mass spectrometry, negative and p ositive chemical ionization mass spectrometry together with mass spect ra analyses of the water-soluble and ether-soluble products obtained b y methanolysis has shown that, in addition to palmitic and stearic aci d residues, the presence of glycerol, ribitol, cholinephosphate and ho moserinephosphate residues. It is suggested that the apparent structur e of compound X is either a phosphatidylcholine attached via a phospho triester bond to a ribitolphosphohomoserine moiety or a phosphatidylho moserine attached via a phosphotriester bond to a ribitolphosphocholin e moiety. The major molecular species is the dipalmitoylderivative (M( r) 1038),whereas the minor molecular species is a stearoyl palmitoyl d erivative (M(r) 1076).