Polydispersity of cartilage proteoglycans. Structural variations with size and buoyant density of the molecules

Proteoglycan monomers were subfractionated according to buoyant density by dissociative CsCl density gradient centrifugation. It was shown that with decreasing buoyant density of the proteoglycan subfraction: (a) the average sizes of the molecules decreased (shown by Sepharose 2B chromatography); (b) the relative content of chondroitin sulfate decreased; (c) the relative content of protein increased; (d) the relative proportion of the amino acids glycine and serine, which occur close to the chondroitin sulfate-peptide linkage, decreased; (e) the relative proportion of the hyaluronic acid-binding region released by treatment of proteoglycans with cyanogen bromide increased; (f) the relative content of the keratan sulfate-enriched region increased. The data indicate that proteoglycans contain a nonvariable hyaluronic acid-binding region, a keratan sulfate-enriched region and a chondroitin sulfate-enriched region of variable size. It is concluded that proteoglycans vary in size mainly because of variations in the size of the chondroitin sulfate-enriched region. Additional data were obtained using subfractions of proteoglycan monomers isolated according to size differences by using Sepharose 2B chromatography. The Kav values of the subfractions on Sepharose 2B ranged from 0 to 0.54. Analyses of these subfractions showed the same variations with size of the content of chondroitin sulfate, protein, amino acids, hyaluronic acid-binding region, and keratan sulfate-enriched region, as was shown for the subfractions isolated at different buoyant densities in the dissociative gradient.