Proteoglycans of rabbit corneal stroma. Isolation and partial characterization.

Proteoglycans extracted from rabbit corneal stroma can be separated by ion exchange and gel chromatography into two proteokeratan sulfates (PKS-I, PKS-II) and two proteodermatan sulfates (PDS-I, PDS-II). PKS-I (21% of the total glycosaminoglycans) contains 48% protein, and PKS-II (43% of the total) has 57% protein. In both, the only hexosamine is glucosamine, 7% of which is found in oligosaccharides. There is much more sialic acid in the oligosaccharides of PKS-II than of PKS-I, and the amino acid compositions of the two proteoglycans differ significantly. The keratan sulfates isolated from them by papain digestion are different in size, but both are digested by endo-beta-galactosidase. PDS-I (30% of the total glycosaminoglycans) has 32% protein, and 35% of its uronic acid is iduronic acid. PDS-II (6% of the total) has 42% of its uronic acid as iduronic. In general, the four rabbit proteoglycans resembled those of human and bovine corneal stroma in being smaller and more protein-rich than those of cartilage.