Isolation and Characterisation of Glycoproteins from Sputum

Sputum has been separated into a sol and a gel phase by ultracentrifugation and the components of these phases examined. A glycoprotein of high molecular weight as well as serum albumin, immunoglobulin A, α1 acid glycoprotein and lactoferrin were detected in the sol phase by gel filtration and immunodiffusion studies. A glycoprotein of similar chemical composition was isolated from the gel phase by solubilisation in 6 M urea/0.1 M NaCl followed by fractional precipitation with ethanol. The carbohydrate content of this glycoprotein, termed the bronchial glycoprotein, varied from 58% (w/w) to 69% (w/w) with sputum from different patients and was composed of fucose, galactose, galactosamine, glucosamine and N‐acetylneuraminic acid. Serine, threonine and proline constituted 44% (w/w) of the amino acid residues of the bronchial glycoprotein and an alkaline borohydride cleavage study indicated that O‐glycosidic linkages exist between N‐acetylgalactosamine and the hydroxyamino acids in the peptide core. Fractionation of the bronchial glycoprotein on DEAE‐Sephadex A‐25 yielded fractions enriched in sulphate and sialic acid but separate fuco, sialo and sulpho glycoproteins were not obtained