We characterized the chemical composition of mucins secreted by ferret tracheal explants and the activities of key mucin glycosyltransferases in ferret tracheal epithelium during a period of rapid postnatal maturation of the mucin-secreting structures. Ferret tracheal explants secrete three major groups of high molecular weight glycoconjugates: (1) those susceptible to bovine testicular hyaluronidase; (2) those resistant to hyaluronidase and exhibiting high density (ρ ≥ 1.60 g/mL); and (3) those resistant to hyaluronidase and exhibiting low density (1.45 ≤ ρ < 1.60 g/mL). The hyaluronidase-resistant, low-density glycoconjugates have typical mucin properties and constitute 36% of total glycoconjugates released in newborns but only 8% in adult ferrets. Mucin secretory rate per unit surface area of trachea progressively decreases with age. Mucin amino acid and total carbohydrate contents do not vary; however, the sialic acid content increases, and fucose content as well as blood group A activity of the mucins decreases with age. Four glycosyltransferases involved in mucin biosynthesis [Galβ3GalNAc:(GlcNAc-GalNAc)β6 N-acetylglucosaminyl-, GalNAc:β3 galactosyl-, Gal:α2 fucosyl-, and GalNAcα2→6 neuraminyltransferase] are present in tracheal epithelium of ferrets at all ages. Activities of all but the neuraminyltransferase decrease with age. The relatively greater neuraminyltransferase activity is consistent with increased incorporation of sialic acid into secreted mucins over the same age span. Conversely, diminution of fucosyltransferase relative to galactosyltransferase activity may contribute to the lower fucose content and lower blood group A activity of mucins secreted by mature ferret tracheas. We speculate that these age-related differences in biosynthetic enzymes, mucin properties, and mucin secretory rates are likely to be reflected in properties of airway surface liquids and their protective functions.
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