Proteoglycans from bovine fetal epiphyseal cartilage. Sedimentation velocity and light scattering studies of the effect of link protein on proteoglycan aggregate size and stability.

Proteoglycan monomer and link proteins were isolated from bovine fetal epiphyseal cartilage and characterized. The physical characteristics of proteoglycan monomer were: s0(20) = 21.3 S, D0t,z = 4.25 x 10(-8)cm2/sec, Mw = 3 x 10(6) and Rg,z = 980A. Link protein preparations contained link proteins 1 and 2, but little or none of the fragment, link protein 3. Link protein-stabilized and link protein-free proteoglycan aggregates were reassembled from proteoglycan monomer, link protein and hyaluronate. The effect of epiphyseal cartilage link protein on aggregate size and stability was examined in sedimentation velocity studies. Compared with link protein from mature bovine nasal and articular cartilages, which contain appreciable amounts of link protein 3, epiphyseal cartilage link protein dramatically stabilized aggregates at pH 5. In the presence of link protein, 92% of the proteoglycan monomers were bound as aggregate at pH 7, and 81% were bound at pH 5. In the absence of link protein, 51% of monomers were bound at pH 7, and only 32% were bound at pH 5. The progressive dissociation of link protein-free aggregates as a function of decreasing pH, and of increasing temperature, was also examined in dynamic light scattering studies. The results of the light scattering studies were in perfect accord with the results of the sedimentation velocity studies. However, compared with the sedimentation velocity studies, the dynamic light scattering studies provided a more detailed and informative description of the dissociation of the link-free aggregate as a function of pH, as a function of temperature, and of the capacity of link protein to stabilize aggregate against dissociation at decreased pH or elevated temperature.