Binding of basic proteins to glycoproteins in human bronchial secretions.

1. Secretions were aspirated from a patient with no history of pulmonary disorder. 2. Mucus glycoproteins, which exhibited blood group A activity, were separated into cetyltrimethylammonium bromide (cetavlon)- and ethanol-precipitable fractions. 3. The cetavlon-precipitable mucin was pure by analytical ultracentrifugation and upon chemical analysis had a composition typical for mucin preparations. 4. The fraction that precipitated with ethanol was found to bind tightly to proteins of a basic nature from which it could be separated by using 6 M urea. 5. This non-covalent interaction may explain the lack of precipitation of this mucus glycoprotein by cetavlon. 6. These basic proteins may be important in determining the rheological behavior of mucociliary secretions.