Glycoconjugates monosaccharides

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

Honda and coworkers used 4 M hydrochloric acid for 6 h at 100° for the hydrolysis of nondialyzable glycoconjugates when determining amino monosaccharides, but preferred 2 M CF3CO2H for 6 h at 100° when determining the neutral monosaccharides and uronic acids, as these compounds are subject to more-severe degradation by 4 M hydrochloric acid. They obtained complete hydrolysis (with >90% recovery of monosaccharides added prior to hydrolysis) by using these two sets of hydrolytic conditions. 

The pathway of the biosynthesis of Neu5Ac demonstrates the origin of sialic acids from the cellular hexose and hexosamine pools. These sugars are, therefore, suitable components for the study of the biosynthesis of sialic acid. However, only ManNAc has been shown to be a relatively specific precursor of sialic acids, as may be seen from the distribution of radioactivity between the individual monosaccharides of glycoconjugates after incubation. Injections of radioactive ManNAc into animals, or incubation of surviving tissue slices or individual cells with this compound, give incorporation of label mainly into the sialic acids.226 227... 

On the other hand, the enzymatic synthesis of glycoconjugates and oligosaccharides leads to high product yields in a short time by stereo- and regioselective one-step reactions. All enzymatic reactions are easy to scale up and are carried out in aqueous media under mild conditions. A whole set of enzymes is now available to build up OAT bonds in monosaccharides, COP bonds in activated monosaccharides e.g. phosphorylated sugars or nucleotide sugars, and C-O-C bonds in di- and oligosaccharides (Fig. 1). However, all these enzymatic reactions are limited by the substrate spectrum of the individual enzyme. 

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