Sedimentation behavior of native and reduced apolipoprotein A-II from human high density lipoproteins

Abstract
The solution properties of human serum apolipoprotein A-II, in the native and reduced forms, were investigated by the technique of sedimentation equilibrium in the analytical ultracentrifuge. For both proteins the apparent weight average MW determined in neutral buffer systems were dependent on protein concentration and invariant with the rotor speeds used (16,000-44,000 rpm) indicating a reversible self-association. These results were independent of temperature between 5-30.degree. C. The pattern of self-association of native apolipoprotein A-II could best be described by a monomer-dimer-trimer equilibrium in agreement with previously reported data. The self-association pattern of apolipoprotein A-II reduced in the presence of 50 mM dithiothreitol conformed with a monomer-dimer-tetramer equilibrium similar to that reported for the native single chain apolipoprotein A-II of the rhesus monkey but differing significantly from that reported for the reduced and carboxymethylated human product.