Distribution studies of proteoglycan aggregates by ultracentrifugation

The tendency forcartilage proteoglycans to aggregate or disperse in ultracentrifugation at high ionic strength is influenced by cations. Guanidinum, Li+ and Ca++ promote disaggregation and Na+, K+ and Cs+ support aggregation. The process of disaggregation is fundamentally the separation of low density from high density proteoglycans, the density being an inverse function of the protein content. PPL 5 pellet formation is a packing or aggregation phenomenon occurring well below the isopycnic density of proteoglycan which accounts for its difference from the isopycnic density equilibrated complex. Cations which promote disaggregation result in shifts in distribution of the proteoglycans on equilibrated density gradients. Comparisons of the desulfated products of the high density aggregated and disaggregated complexes and of more selective high and low density proteoglycan fractions clearly show the heterogeneity of proteoglycans related to protein content. It is suggested that the nature of the variable population of proteoglycan macromolecules permits its existence as a self aggregating system.