Glycosphingolipids sugar moieties

Glycosphingolipids or cerebrosides, which are ceramides with the terminal hydroxyl linked by a glycosidic bond to a sugar moiety, can be handled by MS and GC-MS [285]. Among the sources of glycosphingolipids, characterised with the help of MS, are the membranes of human erythrocytes [300], CSF [301] and from the pancreas of a patient with Fabry s disease [302]. 

On the other hand, the sugar moiety of the glycosphingolipids represents the hydrophilic part of the molecule. The solubility in water is also dependent on the number of monosaccharide residues bound in the molecule. Furthermore, such strongly anionic components as neuraminic acids, and sulfate or phosphate groups, influence the ratio of the solubility in water and fat. These two kinds of solubility characteristics are probably essential in the biological roles of the glycosphingolipids when they function as biomembrane components. 

Mass spectrometry of per(trimethylsilyl)ated derivatives has enabled partial characterization of oligosaccharides obtained from cell walls of Mycobacterium tuberculosis and seeds of Aesculus hippocastanum L.i28b q-jjg structures of the oligosaccharides were then fully elucidated by the use of other chemical and spectroscopic methods. The mass spectra have been determined for a number of neutral and mono- and di-sialo glycosphingolipids as their per(trimethylsilyl) derivatives. At present, m.s. gives only limited information about the sequential order and the nature of the sugar moieties in this type of compound. 

An important group of glycolipids are acidic glycosphingolipids, which contain either bound sialic acid or sulfuric acid. They were previously called mucolipids. The sugar moiety is sulfated in sulfoglycosphingolipids for example, in glycosyl-ceramide sulfates (Figure 5.5.1). 

Gangliosides are a class of glycosphingolipid characterized by the presence of one or more sialic acid residues. They are located in the cell membranes, particularly in the plasma membrane, of almost all cell types. They are anchored in the membranes through their ceramide moiety and have the polar sugar-containing group in the extracytoplasmic side. They are particularly abundant in the nervous system where their expression pattern is modulated during development. 

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