Glycosphingolipids sphingosine

Cerebrosides are major constituents of the membrane of brain cells. They are the simplest glycosphingolipids, serving as model substances for more complex lipids of this kind. Furthermore, they are credited with important properties as receptors for hormones and toxins.29 Schemes 4 13 and 4 14 provide a method for preparing sphingosine and its analogs that can be used for the synthesis of cerebroside compounds. 

Measurements of the quantities of glycolipids inserted into the membrane have also been reported by a technique based on the use of C-labeled lipid anchors. In this method, the carbohydrate (a-o-Man) was covalently coupled to the anchor at the surface of a pre-formed vesicle. Indeed, the liposome structure was shown to remain intact in the treatment. Nevertheless, the measurement of the incorporated mannose was performed after separation of bound and unbound material by centrifugation. The yields of coupling were shown to increase with the increase of the initial mannose/ C-anchor ratio, but non covalent insertions were displayed at high initial mannose concentrations. Therefore, the aforementioned method was not as accurate as could have been expected for the use of radioactive materials [142]. Radiolabeled phospholipids were also used for such determinations thus the amounts of glycosphingolipids incorporated into liposomes were quantified by the use of H-phospholipids whereas the amounts of glycolipids were determined by a sphingosine assay [143]. 

The glycosphingolipids of mammals are known to be cellular-membrane components,1"5 organized in such a way that their lipid moiety, namely, acylated sphingosine (usually called ceramide), is submerged into the outer leaflet of the plasma-membrane bilayer, and contributes to its structural... 

Structural studies of glycosphingolipids involves determination of the structure of the oligosaccharide chain and of the lipid moiety. For the oligosaccharide chain, it is necessary to determine the composition, molar ratio, and sequence of the monosaccharides, their pyranose or furanose nature, and the position of glycosidic bonds and their configuration for the lipid moiety, the composition of the fatty acids and sphingosine bases must be determined. Used for these purposes are the classical, chemical methods, conventionally accepted in the chemistry of carbohydrates and lipids and based on the degradation of compounds, enzymic, and physicochemical methods, primarily mass spectrometry and n.m.r. spectroscopy. 

Sphingosine bases are usually isolated from glycosphingolipids by treatment with methanolic HC1 containing some water,148 and characterized, in the form of the free bases or their 2,4-dinitrophenyl (DNP) derivatives,149 151 by t.l.c. For quantitative determination of bases, a colorimetric procedure is used, based on color formation of the base with Methyl Orange.152 The composition of the sphingosine bases, as their Me3Si derivatives, is determined by g.l.c. and g.l.c.-m.s.,148,153,154 as well as by using for this purpose... 

Precoated silica gel plates (silica gel 60) were purchased from Scientific Products. Bio-Sil A (200 - 400 Mesh) was obtained from Bio-Rad Laboratories. Fatty acid methyl esters, sphingosine and dihydrosphingosine were products of Supelco, Inc. as were 10% DEGS-PS, 3% SP-2340 and 3% OV-17 (all on Supelcoport support). N-acetyl and N-glycolyl neuraminic acid, DEAE-Sephadex A50 and neuraminidase type IX were obtained from Sigma Company. Ganglio-side standards from human brain and neutral glycosphingolipid standards from bovine erythrocytes were prepared in this laboratory. 

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