title: Interaction of lipoprotein lipase with phospholipid vesicles. Role of apolipoprotein C-II and heparin.
abstract: Lipoprotein lipase is bound to heparin-like molecules at the surface of capillary endothelial cells. For maximal activity, the enzyme requires apolipoprotein C-II, a protein constituent of triacylglycerol-rich lipoproteins. In this report, the interactions of apolipoprotein C-II, heparin and sonicated vesicles of dipalmitoylphosphatidylcholine with purified bovine milk lipoprotein lipase were studied by gel filtration on Bio-Gel A5m. In the presence of vesicles of dipalmitoylphosphatidylcholine (1 mg), lipoprotein lipase (25 micrograms) associated with phospholipids even in the absence of apolipoprotein C-II. With limited phospholipid (40 micrograms), the amount of enzyme which associated with lipid decreased in the presence of apolipoprotein C-II (20 micrograms). Human plasma apolipoprotein C-III, another protein constituent of triacylglycerol-rich lipoproteins, also caused a decrease in the amount of enzyme associated with phospholipid. These results suggest that apolipoprotein C-II does not increase the activity of the enzyme by facilitating its interaction with a lipid interface. In the absence of lipid, lipoprotein lipase and apolipoprotein C-II (molar ratio, 1 : 1) eluted from Bio-Gel A5m as two separate components. The interaction of heparin with lipoprotein lipase was studied using a specific [3H]heparin, which was isolated by affinity chromatography on immobilized lipoprotein lipase; the [3H]heparin eluted with 0.6 M NaCl. Specific [3H]heparin coeluted with lipoprotein lipase when the enzyme was associated with phospholipid; the [3H]heparin was released from the enzyme by 0.75 M NaCl.
mesh_terms: D000818:Animals; D053304:Apolipoprotein C-II; D001053:Apolipoproteins / Q000494:pharmacology*; D001056:Apolipoproteins C; D002417:Cattle; D002850:Chromatography, Gel; D006493:Heparin / Q000494:pharmacology*; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000302:isolation & purification / Q000378:metabolism*; D008081:Liposomes; D008297:Male; D008892:Milk / Q000201:enzymology; D011663:Pulmonary Surfactants
chemical_list: D053304:Apolipoprotein C-II; D001053:Apolipoproteins; D001056:Apolipoproteins C; D008081:Liposomes; D011663:Pulmonary Surfactants; D006493:Heparin; D008071:Lipoprotein Lipase