ISOLATION AND CHARACTERIZATION OF HUMAN LP-B LIPOPROTEIN CONTAINING APOLIPOPROTEIN-B AS THE SOLE APOLIPOPROTEIN

A sequential immunoaffinity chromatography procedure was developed to isolate from whole normolipidemic human plasma a subpopulation of apoB containing particles (Lp-B) which is virtually free of non apoB protein. The absence of non apoB protein in Lp-B was assessed by enzyme immunoassay against apolipoproteins A-I, A-II, A-IV, E, C-III and (a). Electron microscopy and fractionation of the isolated particles by gel filtration demonstrated that these particles were heterogeneous in size. However, most of them had diameters between 18 and 26 nm. These particles were found to be rich in cholesterol (molar ratio cholesterol/apoB = 2246 +/- 995) poor in triacylglycerol (molar ratio triacylglycerol/apoB = 555 +/- 518) and had a phosphoslipids/apoB, E molar ratio of 713 +/- 348. Most of the cholesterol was esterified (66% +/- 5%). Lp-B particles bound to the apoB, E receptor of HeLa cells with a lower affinity than LDL prepared by ultracentrifugation (1.030 kg/l < d < 1.053 kg/l). (K(D) = 18.9 vs 10.5 nmol/l).