MOST OF THE LIPID IN PURULENT SPUTUM IS BOUND TO MUCUS GLYCOPROTEIN

Mucus glycoprotein (mucin) is the principal biochemical constituent of sputum. Appreciable quantities of lipid, DNA, and nonmucin proteins a re also present, particularly in purulent sputum. Previous studies hav e shown that purified mucin from respiratory tract secretions contains non-covalently bound lipid. However, it is not known whether lipids i n purulent sputum are associated only with mucin or with nonmucin prot eins and DNA as well. Purulent sputum was obtained from cystic fibrosi s patients. Tracheal aspirates were obtained from noncystic patients w ith purulent secretions due to Pseudomonas species, as well as from no ninfected, noncystic patients who bad mucoid airway secretions. The li pid content of unfractionated airway secretions (sputum or tracheal as pirates), gel filtration-purified mucin, and nonmucin components of th e airway secretions was analyzed. The purified mucin from all three gr oups bad a significantly higher content of solvent-extractable lipid a s compared to unfractionated airway secretions. The nonmucin fractions contained only small amounts of lipid. Density gradient centrifugatio n verified that the lipid recovered in the purified mucin fraction was complexed with the glycoprotein. The results of this study indicate t hat most of the lipids in purulent sputum are associated with mucin.