Sedimentation Properties of Dextran Sulfate-Low Density Lipoprotein Complexes

The nature of interaction between dextran sulfate and the human plasma low density lipoproteins of S_f 0–10 was investigated in high density media of glycine and glucose. The soluble complex formation between the two components was manifested by sedimentation of the lipoproteins along with dextran sulfate in the glycine and glucose media of density 1.063. The addition of sodium chloride to the mixture caused dissociation of the complex: during subsequent ultracentrifugation, flotation of lipoprotein and sedimentation of dextran sulfate occurred. However, when the complex is in the acidic glycine medium (pH 4.0), the addition of sodium chloride did not induce dissociation of the complex.

Both the solubility and the size of the complex were greatly influenced by the ratio of the two components in solution. At low relative concentrations of dextran sulfate, insoluble aggregates were formed; but the aggregates disintegrated into soluble units upon increasing the dextran sulfate concentrations. From the sedimentation patterns of dextran sulfate lipoprotein mixtures at various ratios, it was possible to estimate the ratio of the two components in the complex. In the presence of excess dextran sulfate a composite biphasic Schlieren diagram was produced as a result of the unusual Johnston-Ogston effect.