Ganglioside isolation

Fig. 14.—Schematic Representation of the Fragmentation Observed in the Positive F.a.b.-Mass Spectrum of a Permethylated Ganglioside Isolated from Granulocytes. [Other glyco-sphingolipids fragment in a similar way. Major cleavages are shown with solid lines, and minor cleavages with dotted lines. The masses of ions resulting from cleavages (a), (b), and (c) define the type of sphingosine and the type of fatty acid. In this example, (a) is 548, (b) is [M + H] minus 238, and (c) is [M + H] minus 533.]...

Fig. 3.—Mass Fragmentography of Methylated Neuraminic Acids. [Detection at m/e 274 A, disialosyl-lactosylceramide B, the disialosyl ganglioside isolated C, B after treatment with neuraminidase D, the fraction containing the trisialosyl ganglioside. Detection at m/e 330 E, the disialosyl ganglioside F, the trisialosyl fraction. The peaks identified are (1) the permethylated (terminal) N-acetylneuraminic acid, and (2) the 8-O-acetyl (8-O-substituted) derivative of the methylated N-acetylneuraminic acid. Conditions 1% of SE-30, at 240°. Reproduced, by permission, from Ref. 80.]...

Nevertheless, chemical characterization of the first gangliosides isolated by these methods led to the identification of their constituent parts. Thus, on hydrolysis, sphingosine, fatty acids, N-acylneuraminic acid, and sugars were obtained. 

The fatty acid linked to the amino group of the sphingosine or sphinganine part may also differ, but, in the gangliosides isolated bom nervous tissues, the main fatty acid is stearic acid (80-90%) and, in the gangliosides of spleen and erythrocytes,178 tetracosanoic acid (docosanoic acid, tetracosenoic acid). 

The last-mentioned compound (76) can be obtained from the neuraminidase-resistant ganglioside-G/ by mild hydrolysis with acid (50 mM sulfuric acid at 80°). This compound is the fundamental tetrasaccharide unit of the main gangliosides isolated from the normal human (and also beef) brain. 

The structure of other natural gangliosides isolated from normal-human and bovine nervous-tissues was determined. These individual gangliosides have, in covalent conjugation, more than one residue of N-acetylneuraminic acid (NANA) that can be split off enzymically with neuraminidase, giving2068 the fundamental ganglioside-G/. 

The preliminary, structural investigations of the lipid material obtained led to the conclusion that these gangliosides have a chemical composition different from those of the gangliosides isolated from... 

The phospholipid and glycolipid contents of the brains, and several other characteristics, of thirty-two species of fish belonging either to the elasmobranches or to the teleosts have been reported, Three gangliosides isolated from the starfish Asterina pectinifera have sialic acid residues present in the interior of the carbohydrate chains. Lactosylceramide and water-soluble materials containing arabinose, galactose, and sialic acids were liberated during attempts to remove the sialic acid residues with acid. 

The structural variations observed in ceramides, cerebrosides and gangliosides isolated from sea stars are numerous and cover the three moieties of which glyco-sphingobpids are formed the sugar moiety, of which a dozen examples have been identified the acid moiety, which is almost always a mixture of a dozen fatty chains of varying lengths, saturated in general but sometimes... 

Like in gangliosides, lactones might be found in some bacterial capsular polysaccharides containing 1-carboxyethylsubstituents. But their identification remains problematic due to the conditions of isolation and preparation of analytic samples. To facilitate their detection by NMR, and in order to determine if the formation or hydrolysis of lactones occurred during analytical procedures, synthetic model substances, 2,3- and/or 3,4-lactones based on gluco-12, manno-13, and galactopyranosides 14 were prepared and characterized by NMR spectroscopy (Fig. 2).20 The relative lactonisation rates in acetic acid-fi 4 and hydrolysis rates in buffered D20 were evaluated. 

The aeylneuraminic acids can be released from their glycosidic linkages either by dilute (aqueous or methanolie) acids or sialidases. Special care must be taken in the isolation of the rather labile, O-acv-lated sialic acids, which arc partially non-susceptible to the action of sialidases. Furthennore, in gangliosides, non-O-acetylated sialic acid residues occur, and these are also more or less resistant towards these enzymes. 

---