Studies on the properties of the inextractable proteoglycans from bovine nasal cartilage

Bovine nasal cartilage was repeatedly extracted with the dissociative solvent, 4 M guanidinium chloride. About 25% of the total tissue proteoglycans could not be solubilized as judged by galactosamine analysis. The inextractable proteoglycan could be at least partially solubilized by treating the guanidine-extracted tissue with reagents which completely or partially degraded the proteoglycan protein core. Digestion with papain or cyanogen bromide completely solubilized the tissue and released all of the galactosamine-containing material while trypsin or hydroxylamine treatment left the cartilage macroscopically unchanged and extracted about 50% of the residual galactosamine. The degradatively solubilized material was compared to that extracted with guanidinium chloride. The papain-released glycosaminoglycan chains from the two proteoglycan preparations were similar with respect to size, degree of sulfation, position of sulfation, and hexosamine content. Furthermore, the fragments released from the cartilage residue by either cyanogen bromide, trypsin, or hydroxylamine treatment were of the same size, as judged by gel chromatography, as those derived from similarly digested guanidine-extracted proteoglycan. Trypsin digestion also released the keratan sulfate-enriched peptide as well as peptides from the hyaluronic acid-binding region. By the methods used, the inextractable proteoglycan appears to be similar to the fraction which is readily soluble under dissociative conditions and thus may be held tightly within the tissue by a nonspecific mechanism(s) such as entanglement in the collagen fibril network.