LIPOPROTEINS CONTAINING APOLIPOPROTEIN A-IV - COMPOSITION AND RELATION TO CHOLESTEROL ESTERIFICATION

In order to investigate the relationship of lipid and apolipoprotein composition to cholesterol esterification in lipoproteins containing apolipoprotein (ape) A-IV, apo A-containing lipoprotein particles were isolated from fresh human plasma using a system of sequential immunoaffinity chromatography. Plasma was first depleted of apo B- and apo E-containing lipoproteins. Four major subpopulations of ape A-containing lipoprotein particles were separated: Lp A-I, Lp A-I:A-II, Lp A-IV and Lp A-I:A-IV:A-II. Lp A-IV and Lp A-I:A-IV:A-II contained less total lipid, less cholesterol and more triacylglycerol than Lp A-I and Lp A-I:A-II. Lp A-IV and Lp A-I:A-IV:A-II contained more sphingomyelin and less phosphatidylcholine than Lp A-I and Lp A-I:A-II and were richer in (16:0 +/- 18:0) saturated fatty acids. Among these isolated lipoprotein particles, Lp A-IV contained the highest lecithin: cholesterol acyltransferase (LCAT) activity per mu g of protein. Cholesterol esterification rates were 2.6 +/- 0.5, 5.3 +/- 0.4 and 0.8 +/- 0.2 mu mol of cholesterol per hour per m,a of lipoproteins for Lp A-IV, Lp A-I and Lp A-I:A-II, respectively. The apolipoprotein and lipid composition and LCAT activity of Lp A-IV suggest that this lipoprotein may be a source of cholesterol esterification in plasma.