Chemical aspects of tracheal glycoproteins

The chemical characteristics of tracheal mucus obtained directly from the epithelial surface of the trachea indicate that the mucus from each animal source consists of a group of sulphated sialic acid-containing glycoproteins. Fractionation of the native glycoprotein from the cat by gel chromatography in the presence of urea and dithiothreitol suggests a value of about 3 X 10(6) for the molecular weights. The chief monosaccharide constituents are N-acetylneuraminic acid, N-acetylglucosamine, N-acetylgalactosamine, fucose and galactose. In the goose tracheal mucin, mannose is present (serum proteins being absent). Doubly labelled cat mucus, obtained by giving Na235SO4 and [3H]glucose simultaneously into the lumen of the trachea, is massively released by parasympathetic agents, e.g. pilocarpine. The resulting mucus has a high content of 35S and is derived largely from submucosal gland cells. Subsequent exposure to an irritant, ammonia, releases a low sulphation fraction, highly labelled with 3H, arising from goblet cells. Evidence supports the view that the overall mucus is composed of mixed secretions, chemically distinct, from different cellular synthesizing sites. Differential nervous stimulation of the various sites may cause far-reaching changes in the chemical and physical properties of the mucus by selective action on the secretion of one or more of the contributing glycoproteins.