Studies on human serum high-density lipoproteins. Self-association of human serum apolipoprotein A-II in aqueous solutions.

Some of the solution properties of pure preparations of human serum high-density apolipoprotein A-II were studied by sedimentation equilibrium ultracentrifugation, conducted at different apoprotein concentrations and at several speeds. The concentration dependence of the apparent weight average molecular weight indicated that apolipoprotein A-II, when dissolved in 0.02 MEDTA (pH 8.6), undergoes self-association. Over a protein concentration range between 0.8 and 1.5 mg/ml, the self-association could best be described by a monomer-dimer-trimer step association, although indefinite self-association could not be ruled out. The equilibrium constants obtained were sufficient to describe the system over the concentration range investigated.