Characterization of inositol lipids from Leishmania donovani promastigotes: identification of an inositol sphingophospholipid.

Inositol lipids account for 15% of the total cellular phospholipids of Leishmania donovani promastigotes. Four major inositol lipids were identified and characterized: phosphatidylinositol (PI), phosphatidylinositol phosphate (PI-P), phosphatidylinositol diphosphate (PI-P2), and an inositol sphingophospholipid (InSL). Diacyl and alkyl acyl PI were identified. The major esterified fatty acids of PI, PI-P, and PI-P2 were similar and unlike those of mammalian inositol glycerolipids. Leishmania inositol glycerolipids contained only trace amounts of arachidonic acid; the major species were C16 and C18 acids. The InSL comprised about 40% of the inositol lipids. The amide-linked fatty acids of InSL were mainly C16 and C18 acids. Differential hydrolysis and nuclear magnetic resonance spectrometry indicated that the InSL had a phosphoryl bond. The major long chain bases of the InSL were identified by gas-liquid chromatography and high resolution mass spectrometry as straight chain C16 and C18 sphingosines. The finding of InSL in Leishmania is of interest because InSL have previously been found only in plants and fungi. Metabolic radiolabeling experiments suggest that this lipid may be a precursor of an antigenic cell surface membrane lipophosphoglycan which is shed into the culture medium by the organism.