Release of carbohydrates from glycoproteins

Sialic acids can usually be liberated from glycoproteins with 0.1 N 

H2SO4 at 80°C for 1 hr (Spiro 1965). This is probably because of the terminal positions of these substances in the carbohydrate moieties of glycoproteins, and the lability of the particular glycosidic bond. Complex polysaccharides containing sialic acids, may require more stringent conditions of hydrolysis such as 2 N methanesulfonic acid in anhydrous methanol (Liu 1972). However, more stringent hydrolysis in aqueous media usually leads to greater destruction of sialic acids. Neuraminidases may also be used to release siahc acids (see Liu 1972). 

The neutral sugars can usually be released from glycoproteins with 

2 N HCl or longer times may be required (see Spiro 1972). Since fucose is in terminal positions in the carbohydrate chains of glycoproteins, and since it is more susceptible to destruction, 0.5 N HCl or shorter times of hydrolysis will usually improve the yield of this sugar. Fucose may be determined by a specific colorimetric test (Spiro 1965). 

The N-acetylhexosamines can usually be quantitatively released (as the hexosamines) from glycoproteins with 4 N HCl at 100°C for 6 hr (Spiro 1972). However, under these conditions the other carbohydrate components will undergo varying amounts of destruction. 

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