HUMAN OCULAR MUCUS - CHEMICAL STUDIES

Crude human ocular mucus, or the mucous glycoproteins fractions GP2 and GP3M derived from it, were analyzed. The amino acid analysis indicated a high proportion of serine and threonine residues and sugar analysis of the acid hydrolysate showed the presence of fucose, mannose, galactose, glucose, galactosamine, glucosamine and sialic acid. The lipid present in crude mucus was almost identical to meibomian secretion and unlike skin surface lipid; it was considered to be derived entirely from mixing of the secretions within the tear film. Chromatography of crude mucus on Sepharose 4B or 6B columns as a means of estimating MW was inconclusive, except to indicate that GP2 has a MW greater than 5 .times. 105. Alkaline hydrolysis and tritiated borohydride reduction of GP2 and GP3M released radioactively labeled oligosaccharide side chains from O-glycosidic linkages to serine or threonine; these were analyzed on a BioGel P2 column. They ranged in length from mono- to tetrasaccharide in GP2, and from a length intermediate between mono- and disaccharide to tetrasaccharide in GP3M, but no sialic acid was present in any of these chains. Calculations based on the relative proportions of chains indicated that almost all serine and threonine residues of the polypeptide bore side chains. Digestion studies on crude mucus showed little breakdown into smaller fragments unless sialic acid had previously been removed.