Physical Properties and Polydispersity of Proteoglycan from Bovine Nasal Cartilage

Abstract

Abstract Eighty per cent of the proteoglycan of bovine nasal cartilage can be recovered in a purified preparation known as proteoglycan subunit; the preparation contains 87% chondroitin sulfate, 6% keratan sulfate, and 7% protein. The physical properties of proteoglycan subunit are not affected by exposure to 4 m guanidinium chloride, to reducing agents, or to pH 2.7. Proteoglycan subunit contains a single class of macromolecules. However, the macromolecules are polydisperse because they exhibit a continuous distribution of sedimentation coefficients. At infinite dilution, 80% of the molecules have sedimentation velocities in 0.5 m guanidinium chloride between 15 and 35 S, with a weight average of 25 S. The macromolecules occupy large, approximately spherical domains in solution; as much as 55 ml of solvent is entrained per g of solute. Combined rheological and centrifugal analyses suggest that the molecular weight polydispersity of proteoglycan subunit is closely approximated by a Gaussian curve with a mean of 2.5 x 106 and a standard deviation of 1.2 x 106. A method is described by which the macromolecules of proteoglycan subunit can be partitioned into three major fractions with approximate average molecular weights of 1.8, 2.5, and 3.0 x 106. In 0.5 m guanidinium chloride, the limiting viscosity numbers of these fractions vary only as the 0.2 power of their molecular weight, a consequence of the fact that the macromolecules are highly branched polymers. Analyses of these fractions suggest that the proteoglycan subunit contains only one type of protein and that polydispersity is the result primarily of differences in the number of chondroitin sulfate chains attached to the protein.