Isolation and partial characterization of low density proteoglycans from bovine articular cartilage

Low density proteoglycans (PG-III) were isolated from bovine articular cartilage by extraction with 4 M guanidinium chloride followed by sedimentation in a dissociative CsCl density gradient and fractionation by chromatography on DEAE-cellulose and Sepharose CL-6B columns. The PG fractions obtained were analyzed to determine the amino acid composition, the content of sulfate and carbohydrate constituents, the molecular weight, and sedimentation properties under associative and dissociative conditions and the types of glycosaminoglycan components. The results show that the major type of low density PG in adult bovine metacarpophalangeal cartilage is a proteochondroitin sulfate with a Mr approximately 44,000. A single glycosaminoglycan component was detected following alkaline borohydride cleavage that was completely digested by chondroitinase ABC treatment. The disaccharide composition of this glycosaminoglycan was 4% O-sulfate, 22% 6-sulfate, and 74% 4-sulfate. Variations were observed in the content of chondroitin sulfate and the other carbohydrate constituents, indicating that the low density PG in this tissue probably occurs as a family of molecules with a variable composition. Sedimentation velocity analysis showed that under associative conditions PG-III formed high molecular weight complexes by self-association.