Mucin-like glycoproteins secreted from cultured hamster tracheal surface epithelial cells: their hydrophobic nature and amino acid composition.

Confluent cultures of primary hamster tracheal surface epithelial cells synthesize and secrete high molecular weight mucin-like glycoproteins (HMW MLGP). Secreted HMW MLGP are highly associated with various lipids, indicating that they are extremely hydrophobic. These HMW MLGP are also associated with varying amounts of "small" glycoproteins via hydrophobic interactions and they can be dissociated by heat and detergent treatments. HMW MLGP free of these "small" glycoconjugates have a buoyant density of 1.5 g/ml and can enter 4% but not 7.5% gels during SDS-polyacrylamide gel electrophoresis. Amino acid composition analysis of HMW MLGP free of these "small" glycoproteins shows that they are relatively rich in serine, threonine, and proline, but the total content of these amino acids seems somewhat lower than that of in vivo airway mucins.