Non-electrostatic factors govern the hydrodynamic properties of articular cartilage proteoglycan

The hydrodynamic frictional resistance to water flow exerted by articular cartilage proteoglycan is shown to be similar to that of proteoglycan isolated from Swarm rat chondrosarcoma, and independent of the state of aggregation of the proteoglycan. Frictional resistance is dependent, however, on the chain segments of the constituent chondroitin-sulphate and keratan-sulphate chains of the proteoglycan. Frictional resistance offered by chondroitin sulphate was independent of pH over the range 3.2-8.7. This confirms previous studies, associated with varying ionic strength and chemical modification of ionic groups of chondroitin sulphate, which showed that the frictional resistance offered by this molecule is independent of electrostatic factors. Water-structure-breaking and hydrogen-bond-breaking solvents were also without major effects on the flow resistance offered by chondroitin sulphate. An overall secondary structure of chondroitin sulphate was not evident, as it showed no significant difference to dextran in terms of its temperature dependence of relative viscosity. Local regions of rigid secondary structure, as manifested through inter-residue hydrogen bonding between sugar residues, is likely to control flow resistance as periodate-oxidized chondroitin sulphate and periodate-oxidized and reduced preparations showed a significant decrease in their frictional resistance to water.