Comparison of structural glycoproteins from mucus of different sources.

The main structural glycoprotein derived from three mammalian mucociliary epithelial secretions (bovine cervical, human lung and human middle ear mucus) were compared. The glycoprotein was purified on a cesium chloride density gradient after prior cleavage of disulphide bonds. Marked similarities were seen for the glycoproteins in their sugar and amino acid composition, in electrophoretic mobility, in sedimentation rate and in their banding densities in a cesium chloride density gradient. The molecular weight of these materials was approximately 0.6-10(6). The similarity noted for these materials occurred despite two of them (lung and middle ear) being derived from pathological sources. The glycoprotein derived from an amphibian mucociliary epithelial secretion (frog palatal mucus) was different; it banded at a lower buoyant density and had a lower sugar content. These findings are discussed in terms of the rheological properties and physiological transport role of mucus on ciliated epithelia. It is suggested that reported differences in the properties of mammalian secretions from different sources is due to differences in the extent of crosslinking between glycoprotein units rather than to chemical or structural differences. In the case of the frog its very different composition may be in keeping with its rather different rheological properties.