Acetylhexosamine

GalNAc, Gal, GlcNAc, Hex and HexNAc are the abbreviations used when discussing sequences of monosaccharides and represent A-acetylgalactosamine, galactose, A-acetylglucosamine, hexose, i.e. a monosaccharide with six carbon atoms, and A-acetylhexosamine, respectively. 

FIGURE 9.4 TLC-blotting/SIMS of various glycosphingolipids. (A) TLC profile of the separated glycosphingolipids, (B) MS profiles obtained by TLC-blotting/SIMS (a) spectrum of sulfatide peaks at m/z 862, 876, 890, 906, and 918 are molecular ions with different fatty acid species indicated in the figure (asterisks are peaks of triethanolamine as matrix) (b) spectrum of Gb Cer peaks at m/z 1309 and 1337 are molecular ions with different fatty acid species as indicated (c) spectrum of G peaks at m/z 1151, 1235, and 1263 are molecular ions with different fatty acid species as shown. Abbreviations LCB — long chain base, FA — fatty acid, hFA — hydroxyfatty acid. Hex — hexose, HexNAc — /V-acetylhexosamine. (From Taki, T. et al.. Anal. Biochem., 225, 24—27, 1995. With permission.) Continued. 

Alkali on the IV-Acetylhexosamines and the Specific Blood-Group Mucoids. Biochem. J. 51, 379 (1952). 

A feasible way of introducing acid-stable linkages into carbohydrates is N-deacetylation. This can be achieved with hydrazine.59,70,71 The use of sodium hydroxide-sodium benzenethioxide in aqueous dimethyl sulfoxide for this purpose has also been described72 The difference in the acid hydrolysis of N-acetylhexosamine-con-taining carbohydrates before and after N-deacetylation was used in the study of complex glycoprotein saccharides from human erythrocyte membranes.73-75 Methylation analysis of the glycopeptides prepared... 

This enzyme [EC 3.2.1.52], also referred to as )3-hexos-aminidase and A-acetyl-/3-glucosaminidase, catalyzes the hydrolysis of terminal nonreducing Ai-acetylhexosamine residues in A-acetyl-/3-hexosaminides. A-Acetylgluco-sides and A-acetylgalactosides are substrates. 

Further developments are shown in Figure 4. On the basis that glucosamine reacted with pyruvic acid in the presence of alkali to yield pyrrole-2-carboxylic acid, in 1% yield, Gottschalk (21) proposed that sialic acid was formed by an aldol condensation reaction between N-ace-tylglucosamine and pyruvic acid. Kuhn and Brossmer (15) and Zilliken and Glick (22) showed that the reverse reaction also took place under alkaline conditions. Cornforth, Firth, and Gottschalk (23) synthesized crystalline N-acetylneuraminic acid (NANA) from N-acetylglucosamine and oxaloacetic acid (pH 11, 20°C). Under conditions less subject to misinterpretation, Heimer and Meyer (24) found that Vibrio cholerae enzymes cleaved NANA into an N-acetylhexosamine and pyruvic acid. 

In this connection Kochetkov and co-workers (73) have reported that hog stomach A + H substance contains several N-acetylhexosamine residues bound by (1 - 3) linkages to the N-acetyl-D-galactosamine residue which is linked to serine or threonine of the peptide backbone, but no oligosaccharides have yet been isolated. 

Gramatikos SI, Valley U, Nimtz M, Conrad HS, Wagner R (1998), Intracellular UDP-V-acetylhexosamine pool affects Ai-glycan complexity a mechanism of ammonium action on protein glycosylation, Biotechnol. Prog. 14 410-419. 

Valley U, Nimtz M, Conradt HS, Wagner R (1999), Incorporation of ammonium into intracellular UDP-activated N-acetylhexosamines and into carbohydrate structures in glycoproteins, Biotechnol. Bioeng. 64 401-417. 

Hex hexose, HexNAc /V-acetylhexosamine, Neu5Ac /V-acetylneuraminic acid, dHex deoxyhexose. This table is adapted from ref. 96. 

Figure 9 Selective ceramide deacylation of N-acetylhexosamine that contains GSLs. Cangliotriaosyl ceramide is shown as example. In organic solvent, 1 N base hydrolysis results in the cleavage of both amides, but acetylation in aqueous buffer only affects the amino sugar.

Sialomucins [Odin (02)] or sialoproteins [Werner (W9)] are another type of mucosubstance found in the stomach. Their carbohydrate moiety is composed of equimolecular amounts of acetylhexosamine (usually galactosamine) and sialic acid. The latter is a group name for several materials derived from the same basic substance, neuraminic acid. In human mucosubstances, the N-acetylneuraminic acid is the main form of sialic acid (FI, F2). In hog stomach, the sialic acid consists of 80%... 

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