Factors influencing the viscous properties of chicken tracheal mucins

1. Reduced viscosities, in water, of different types of mucin, such as fibrillar, gelatinous and soluble phase, separated from chicken tracheal secretions were measured. 2. H-bond breaking agents caused a significant decrease in the reduced viscosity of these mucins, but thiol-reagents alone did not have any effect. 3. Papain and Pronase did not cause any decrease in the reduced viscosity of these mucins. Neuraminidase decreased the reduced viscosity of soluble phase mucin by 50% by removing about 30% of its N-acetylneuraminic acid but had no effect on fibrillar and gelatinous mucins. Sulphatase neither removed any sulphate ester groups nor decreased the reduced viscosity. Due to some nonspecific intermolecular interaction, mixtures of mucins and enzymes or ovalbumin exhibited elevated reduced viscosities. 4. Ionic strength of the solutions appeared to decrease the reduced viscosity of these mucins. Increasing concentrations of Ca²⁺ in solutions of ionic strength of approx. 0.1 caused significant decrease in the reduced viscosity, but had no such effect in solutions of ionic strength of more than 0.1. 5. N-Acetylneuraminic acid and sulphate ester residues were 46.6±0.2, 43.4±0.6, 27.9±3.3 mg/g and 66.0±2.0, 34.2±3.3, 2.5±0.8 mg/g for fibrillar, gelatinous and soluble phase mucins, respectively. There appeared to be a good correlation between viscosity and N-acetylneuraminic acid contents among mucins of low reduced viscosities and between viscosity and sulphate ester residues among mucins of high reduced viscosities.