Isolation and biochemical characterization of the tryptic fragments of bovine nasal-cartilage proteoglycan monomer of high buoyant density.

Relatively homogeneous fractions of proteoglycan fragments were prepared from tryptic digests of the 4M-guanidinium chloride extract of bovine nasal cartilage. Glycosaminoglycan-containing fragments were separated from non-proteoglycan contaminants by ion-exchange chromatography and fractionated by equilibrium density-gradient centrifugation under dissociative conditions. The fractions of highest buoyant density were chromatographed on a column of Sepharose 4B, digested with chondroitinase ABC and chromatographed on a column of Sepharose 6B, yielding two distinct fractions: fraction B/6B-4 contained fragments from the chondroitin sulphate-bearing region of the proteoglycan monomer, and fraction B/6B-2 fragments from the keratan sulphate-rich region, most probably including a chondroitin sulphate-bearing monomer segment. By dansyl chloride analysis, fraction B/6B-2 had alanine and leucine as sole and fraction B/6B-4 had isoleucine and leucine as greatly predominant N-terminal amino acids, indicative of the relative homogeneity of these preparations of cartilage proteoglycan monomer fragments.