Sialic acid salivary mucins

Sialic acids are a family of nine-carbon acidic monosaccharides based on 3-deoxy nonulosonic acid (Fig. 17.4, also see Chapter 5). In 1952, the biochemist Gunnar Blix introduced the term sialic acid from the Greek aaXia (salia) or saliva after isolating this molecule from the salivary gland mucin. Sialic acid is now the generic term for the family that includes derivatives with a C5-amino substituent called neuraminic acid. Neu5Ac (5) is the type of sialic acid found in humans [47],... 

Fig. 30.11. Structure of salivary mucin. The sugars form hydrogen bonds with water. Sialic acid provides a negatively charged carboxylate group. The protein is extremely large, and the negatively charged sialic acids extend the carbohydrate chains so the molecules occupy a large space. All of the salivary glycoproteins are 0-linked. NANA is a sialic acid.

The two sialyltransferase activities have identical pH optima and Grimes (1970) suggests that a single enzyme may be involved. However, the colostrum glycoprotein sialyltransferase and the salivary gland mucin sialyltransferase are believed to be separate enzymes (Roseman et al, 1966), the former attaching sialic acid to terminal galactose resi-... 

The binding of cholera toxin by salivary mucin was inhibited by free sialic acid or by treatment of the mucin with neuraminidase, whereas no inhibition was achieved in parallel experiments with gastric and intestinal mucins. ... 

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