Glycosphingolipids carbohydrate chain structure

Glycosphingolipids with long carbohydrate chains have been isolated from ovine erythrocytes. Their structures were confirmed by the usual techniques and the major component was the Forsman-active glycolipid. Lacto-A -neo-tetraosylceramide was another component and three highly polar glycolipids containing 10-12 sugar residues were also found. 

Glycosphingolipid profiling deals with the structural issues of determining both the carbohydrate and Upid portions. Carbohydrate chains can be either hnear or branched, and can reach up to 50 monosaccharide units in length. Moreover, they can be substituted by rather labile siaHc acids or fucose at different locations. The lipid portion is heterogeneous in the sphingosme base moiety, and can contain different lengths of fatty acids hnked by an amide bond. 

It becomes increasingly evident, that malignant transformation of cells is accompanied by an impaired ability to synthesize more complex oligosaccharide structures, and the level of glycosphingolipids with smaller and incomplete carbohydrate chains may thus be increased. This explains, for example, the preponderance of lactosyl ceramide in certain carcinomatous tissues. Cultured hamster kidney fibroplasts transformed into malignant cells by infection with polyoma virus had low levels of ganglioside Gi c 1, decreased to about 20% of that in normal cells, and increased concentrations of lactosyl ceramide (Hakomori and Murakami, 1968 Hakomori et al.,... 

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. 

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