Evidence for the presence of a low molecular weight proteoglycan aggregation factor in rabbit ear cartilage

Abstract Proteoglycans were extracted from rabbit ear cartlage with 0.15 M NaCl, and with 4 M guanidine · HCl. They were subjected to gel chromatography on Sepharose 2B and 6B either before or after centrifugation in CsCl density gradients. This was to remove a previously described proteoglycan aggregation factor named glycoprotein link (Sajdera, S. W. and Hascall, V. C. (1969) J. Biol. Chem. 244, 77–87 and Hascall, V. C. and Sajdera, W. S. (1969) J. Biol. Chem. 244, 2384–2396). Evidence for at least three aggregation states is presented. The presence of glycoprotein link and an additional aggregation factor (X) is required for the largest aggregates to be formed. In the absence of Factor X, which precipitates at low ionic strength, large aggregates cannot be formed even in the presence of glycoprotein link. In the absence of glycoprotein link, smaller species are formed which can be further dissociated into even smaller units if Factor X is removed. The smallest unit is the only species which can be found in the 0.15 M NaCl extract while in the 4 M quanidine · HCl extract it represents only a minor protion (about 10%) of the total prteoglyacan. Studies on radioactively labeled cartilage suggest that this smallest unit is more recently synthesized than the larger aggregates.