DESORPTION MASS-SPECTROMETRY OF GLYCOSPHINGOLIPIDS

This chapter discusses desorption mass spectrometry of glycosphingolipids (GSLs). Glycosphingolipids, by definition glycosides of the ceramides, occur ubiquitously on the outer leaflet of cell surface membranes of vertebrates and invertebrates. Their carbohydrate moiety may be composed of one up to more than forty sugar residues. The ceramide portion (Cer), composed of a sphingosine base and a fatty acid moiety linked to each other by an amide bond, can vary in type. More than sixty different sphingosine bases have been described so far. The alkyl chains of the fatty acid moiety vary from C14 to C26 and may contain double bonds and/or hydroxy groups. The nomenclature of glycosphingolipids is based on the carbohydrate moiety. A glycosphingolipid thus defined may, however, vary in its lipid portion, depending on species, organ, and cell type. The complete structural elucidation of a glycosphingolipid implies the determination of the following parameters: (1) the molecular weight; (2) the number and the type of sugar components; (3) their sequence and pattern of branching; (4) the sites of linkages; (5) anomeric configuration; (6) the presence of additional functional groups, for example, phosphates and sulfates and their site of linkage; (7) the sphingosine base; (8) the fatty acid moiety; and (9) the conformation of the GSL molecule. © 1990, Elsevier Inc. All rights reserved.