Altered proteoglycan synthesis by epiphyseal cartilages in culture at low SO4(2-) concentration

Proteoglycan Type H formed by incubation of chick embryo epiphyseal cartilages with [14C]glucosamine altered its buoyant density as the concentration of SO4(2-) in medium was lowered from 300 to 0 microM. At the highest SO4(2-) concentration, the labeled product was essentially identical with unlabeled proteoglycan Type H (i.e. the molecules already preformed in ovo) with respect to the buoyant density and hyaluronic acid-binding activity. With decreasing the SO4(2-) concentration in medium, the products showed a gradual decrease in the buoyant density with no apparent change in the hyaluronic acid-binding activity. This change of buoyant density was directly related to a decrease in average sulfation degree of the chondroitin sulfate moiety, which in turn reflected an increase in the ratio of low sulfated chondroitin chains (Chn) to high sulfated chondroitin sulfate chains (CS) per proteoglycan molecule. At intermediate SO4(2-) concentrations, 50 and 100 microM, the labeled products were of hybrid type containing both Chn and CS chains. Treatment of such hybrids with trypsin yielded, in each case, a mixture of CS- and Chn-carrying peptide fragments with an average buoyant density slightly lower than that of the parent proteoglycan. In no case were these fragments separated into two discrete groups corresponding to Chn-rich peptides and CS-rich peptides, respectively, suggesting that the two types of polysaccharide chain are rather evenly distributed along the core protein.