Physicochemical characterization of soluble complexes of human serum low density lipoprotein with heparin

Soluble complexes of low density lipoproteins (LDL) with heparin (HEP) and chondroitin sulphate (CS) in the absence of divalent cations have been studied by means of a micro-rolling-ball ciscometer to obtain information about molecular size and structure of the aggregates. The rheological results were supplied and corroborated by light scattering measurements, electrophoresis and analytical ultracentrifugation. Molar binding ratios were measured using gel filtration assays and ultracentrifugation. At a certain weight ratio of LD To HEP the solutions showed a significant viscosity maximum. At this weight ratio 2–3 LDL particles are held together 1–2 HEP chains. The hydrodynamic radius R_H of this complex is about 16.3 ± 0.90 nm and the rotational diffusion constant is > 7.1 × 10³ s^?1. With excess HEP the radius of the aggregates is almost the same as that of free LDL (R_H = 11.9 ± 0.70 nm). Quantitative binding studies revealed that in this case 1–2 HEP molecules are bound to a single LDL particle. An interaction was also found with CS and LDL but complex formation in this case showed different characteristics. Very low density lipoproteins (VLDL) and high density lipoproteins (HDL) gave no rheologically effective aggregates with HEP.