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

In order to investigate the relationship of lipid and apolipoprotein c omposition to cholesterol esterification in lipoproteins containing ap olipoprotein (ape) A-IV, apo A-containing lipoprotein particles were i solated from fresh human plasma using a system of sequential immunoaff inity chromatography. Plasma was first depleted of apo B- and apo E-co ntaining lipoproteins. Four major subpopulations of ape A-containing l ipoprotein 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 li pid, 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 le ss 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 lipoprotei n particles, Lp A-IV contained the highest lecithin: cholesterol acylt ransferase (LCAT) activity per mu g of protein. Cholesterol esterifica tion rates were 2.6 +/- 0.5, 5.3 +/- 0.4 and 0.8 +/- 0.2 mu mol of cho lesterol 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 LC AT activity of Lp A-IV suggest that this lipoprotein may be a source o f cholesterol esterification in plasma.