Fractionation and partial characterization of macromolecular components from human ocular mucus

Crude human ocular mucus was extracted with 0.154 M-NaCl to separate soluble protein components from mucus. Small amounts of lipoglycoprotein of high molecular weight, as well as twelve plasma proteins, were detected in the soluble extract by gel filtration and immunodiffusion studies. After the NaCl extraction, the remaining mucus residue was further extracted with 6 M-urea-0.2 M-Tris-phosphoric acid buffer. From this portion of soluble extract, a relatively larger amount of lipoglycoprotein of high molecular weight, as well as a lower molecular weight fraction containing eight detectable plasma proteins, were both isolated by gel filtration. The glycoprotein moieties of the lipoglycoproteins of high molecular weight had similar chemical composition. Both contained approximately 40-43% protein and 57-60% carbohydrate, giving a carbohydrate--protein ratio of 1.30 to 1.48. Fucose, galactose, N-acetylhexosamine and N-acetylneuraminic acid comprised about 423 516 residues per 1000 amino acid residues, while serine and threonine constituted about 285 299. All analyses indicated mucin-like character in the lipoglycoproteins of high molecular weight. Plasma proteins constituted approximately three-fifths of the macromolecular components in ocular mucus. These proteins also appeared to be in complexes with lipids, but to a much lesser extent than the high molecular weight fractions. The relevance of present findings to the structure and composition of precorneal tear film is discussed.