Salivary glands, mucin from

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],... 

Wieruszeski, J. M., Michalski, J. C., Montreuil, J., Strecker, G., Peter-Katalinic, J., Egge, H., Van Halbeek, H., Mutsaers, J.H.G.M., and Vliegenthart, J.F.G., 1987, Structure of the monosialyl oligosaccharides derived from salivary gland mucin glycoproteins of the Chinese switlet, J. Biol Chem. 262 6650-6658. 

The genes encoding the polypeptide backbones of a number of mucins derived from various tissues (eg, pancreas, small intestine, trachea and bronchi, stomach, and salivary glands) have been cloned and sequenced. These studies have revealed new information about the polypeptide backbones of mucins (size of tandem repeats, potential sites of N-glycosylation, etc) and ultimately should reveal aspects of their genetic control. Some important properties of mucins are summarized in Table 47-8. 

Food is taken into the buccal cavity, where it is masticated by the teeth and mixed with saliva from three pairs of salivary glands. It moistens the food and dissolves some molecules enabling them to interact with the taste receptors on the tongue. Saliva contains Na% Cl and HCOs ions and a protein, mucin, which is a component of mucus that lubricates the chewed food on its way down the oesophagus. The pH of saliva is about 7.8, which neutralises acid formed by bacteria in the mouth this protects tooth enamel... 

Submucosa. The submucosa is a relatively dense connective tissue with a few accessory salivary glands (mucus acinus).102 The saliva is secreted primarily by parotid, submandibular, and sublingual glands at a rate of 0.5 to 2 L/day.94 Apart from water, saliva is composed of electrolytes, mucin (forms mucus with water), amylase, lysozyme (a bacteriostatic enzyme), IgA antibodies, and metabolic wastes such as urea and uric acid.18 The pH of saliva varies between 6.8 and 7.2.96... 

Enzymes, glycoproteins, and mucins secreted from the salivary glands, stomach, intestine, biliary tract, and pancreas, which together constitute about 20-30 g/day ... 

In Tn-syndrome the sialyl transfer must also be defective, but Dahr etaL could not measure it and have suggested that the enzyme in erythrocyte and leucocyte membranes differs from that in submaxillary salivary gland in requiring Gaipi,3GalNAxal-Ser as its substrate. Hence the structure produced by the sialyl transfer would be a trisaccharide, not a disaccharide, as in salivary mucins. In that case Tn-syndrome would require only one, and not two, enzyme defects. 

Most proteins found in membranes of mammalian cells are glycosylated. This holds, in particular, for the mucins which are expressed by most types of epithelial cells, e.g. in the salivary gland, hreast, liver, pancreas etc The glycans of glycoproteins not only influence physicochemical properties of these macromolecules and protect the proteins from enzymatic degradation, but also play key functions in processes such as cell adhesion, cell differentiation and cell recognition. 

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