Characteristics of the nonaggregating proteoglycans isolated from bovine nasal cartilage.

Purified proteoglycans from bovine nasal cartilage (the Al fraction) were separated by sedimentation velocity centrifugation into a fraction enriched in aggregates (Al-Sl) and a fraction of nonaggregated proteoglycans (Al-S2), containing about 85% and 15% of the starting material, respectively. Both fractions were centrifuged in a dissociative CsCl density gradient to remove non-proteoglycan proteins. Proteoglycans from Al-S2 had (a) a lower buoyant density; (b) a lower content, both relative and absolute, of keratan sulfate; (c) a lower absolute content of chondroitin sulfate; (d) a higher ratio of chondroitin sulfate to keratan sulfate; (e) a higher protein content; and (f) a smaller hydradynamic size than for the Al-S1 proteoglycans. While essentially all the proteoglycans from Al-S1 were able to interact with hyaluronic acid, only about 30% of those from Al-S2 could interact. Those proteoglycans in Al-S2 which did not interact with hyaluronic acid, the nonaggregating proteoglycans, were purified. They had a higher content of protein, which was enriched in serine and glycine, residues localized in the chondroitin sulfate rich region. Their contents of chondroitin sulfate, keratan sulfate, and the keratan sulfate-rich region were considerably lower than for the aggregating proteoglycans. A larger proportion of low molecular weight peptides without bound polysaccharide was released by trypsin digestion of the nonaggregating proteoglycans compared with the aggregating proteoglycans. Trypsin digests of aggregating proteoglycan monomers and of purified hyaluronic acid-binding region contained a relatively large molecular size polypeptide which was not present in nonaggregating proteoglycans. In sum, the nonagg-regating proteoglycans have many structural features different from aggregating proteoglycans and are unlikely to be derived from the aggregating proteoglycans by a simple degradation process.