Electron microscopy of mucin from sputum in chronic obstructive bronchitis

Sputum from patients with chronic obstructive bronchitis has been fractionated on Sepharose columns after treatment with urea 6 mol/l at pH 12.5 followed by neutralization. The "mucin" fraction, which contained 70% carbohydrate and 30% protein was studied in the electron microscope after staining with phosphotungstic acid. Positively stained, thread-like, irregular contours of the mucin molecules could be demonstrated with lengths varying from 2,000 to 5,000 nm, corresponding to molecular weights between 2 X 10(6) and 6 X 10(6). This correlates fairly well with estimates from the literature of the size of these molecules.