Comparison of four procedures for separating apolipoprotein A- and apolipoprotein B-containing lipoproteins in plasma.

Because lipoproteins containing apolipoprotein A (ApoA-I + ApoA-II) or apolipoprotein B (ApoB) seem to exert opposite effects as risk factors for coronary heart disease, we decided to determine the separability of these two major plasma lipoproteins by procedures originally designed to separate high-density from low- and very-low-density lipoproteins. The presumably ApoB-free lipoproteins isolated from normal plasma by (a) ultracentrifugation at d = 1.063; precipitation with (b) heparin-Mn2+ or (c) phosphotungstate-Mg2+; or (d) immunoprecipitation with antibodies to ApoB were characterized by quantifying cholesterol and apolipoproteins A-I, A-II, B, C-II, C-III, D, E, F, and Lp(a). ApoA- and ApoB-containing lipoproteins were completely separated only by immunoprecipitation with antibodies to ApoB. The ApoB-containing lipoproteins isolated by other procedures always contained 4% to 20% of total plasma ApoA-I and differed substantially from one another with respect to the content of some of the minor apolipoproteins. Measuring apolipoproteins was more reliable than measuring cholesterol for monitoring this separation and for expressing the concentrations of ApoA- and ApoB-containing lipoproteins.