PREPARATION AND CHARACTERIZATION OF SPHEROIDAL, RECONSTITUTED HIGH-DENSITY-LIPOPROTEINS WITH APOLIPOPROTEIN-A-I ONLY OR WITH APOLIPOPROTEIN-A-I AND APOLIPOPROTEIN-A-II

This study describes the preparation of spheroidal reconstituted HDL w hich contain apolipoprotein (apo) A-I only, (A-I w/o A-II) r-HDL, or a po A-I and apo A-II, (A-I w A-II) r-HDL. Spheroidal (A-I w/o A-II) r-H DL with diameters of 8.0, 9.2 and 11.2 nm were prepared by incubating discoidal (A-I w/o A-II) r-HDL with lecithin-cholesterol acyltransfera se and low-density lipoproteins. Spheroidal (A-I w A-II) r-HDL were pr epared by displacing apo A-I from spheroidal (A-I w/o A-II) r-HDL with apo A-II. Modification with apo A-II did not significantly affect the diameters of the 8.0 and 9.2 nm (A-I w/o A-II) r-HDL. When, however, apo A-II was added to the (A-I w/o A-II) r-HDL of diameter 11.2 nm, th e size of the particles decreased to 9.4 nm. To determine whether modi fication of (A-I w/o A-II) r-HDL with apo A-II altered the structure o f the r-HDL, the packing of phospholipids in the modified and unmodifi ed particles was compared by steady state fluorescence polarization an d the environments of the apo A-I tryptophan residues in (A-I w/o A-II ) and (A-I w A-II) r-HDL were compared by fluorescence spectroscopy. T he results of these studies suggested that modification of spheroidal (A-I w/o A-II) r-HDL with apo A-II alters the environment of apo A-I t ryptophan residues in small, but not large, r-HDL and does not affect the packing of phospholipids.