title: Interaction of synthetic peptides of apolipoprotein C-II and lipoprotein lipase at monomolecular lipid films.
abstract: The triacylglycerol hydrolyase and phospholipase A1 activities of bovine milk lipoprotein lipase toward long-chain fatty acyl ester substrates were investigated with monomolecular lipid films containing trioleoylglycerol and phosphatidylcholine. In a monolayer of egg phosphatidylcholine containing 3 mol% [14C]trioleoylglycerol, and in the presence of apolipoprotein C-II, a 79 amino acid activator protein for lipoprotein lipase, enzyme activity was maximal at a surface pressure of 21-22 mN X m-1 (37 mumol oleic acid released/h per mg enzyme); enzyme activity was enhanced 9-fold by apolipoprotein C-II. At surface pressures between 22 and 30 mN X m-1, lipoprotein lipase activity decreased over a broad range and was nearly zero at 30 mN X m-1. Apolipoprotein C-II and the synthetic fragments of the activator protein containing residues 56-79, 51-79 and 44-79 were equally effective at 20 mN X m-1 in enhancing lipoprotein lipase catalysis. However, at surface pressures between 25 and 29 mN X m-1, only apolipoprotein C-II and the phospholipid-associating fragment containing residues 44-79 enhanced enzyme catalysis. The effect of apolipoprotein C-II and synthetic peptides on the phospholipase A1 activity of lipoprotein lipase was examined in sphingomyelin:cholesterol (2:1) monolayers containing 5 mol% di[14C]myristoylphosphatidylcholine. At 22 mN X m-1, apolipoprotein C-II and the synthetic fragments containing residues 44-79 or 56-79 enhanced lipoprotein lipase activity (70-80 nmol/h per mg enzyme). In contrast to trioleoylglycerol hydrolysis, the synthetic fragments were not as effective as apolipoprotein C-II enhancing enzyme activity towards di[14C]myristoylphosphatidylcholine at higher surface pressures. We conclude that the minimal amino acid sequence of apolipoprotein C-II required for activation of lipoprotein lipase is dependent both on the lipid substrate and the packing density of the monolayer.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D053304:Apolipoprotein C-II; D001056:Apolipoproteins C / Q000138:chemical synthesis* / Q000378:metabolism; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D005260:Female; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008892:Milk / Q000201:enzymology; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism; D054466:Phospholipases A1; D013499:Surface Properties; D014304:Triolein / Q000378:metabolism
chemical_list: D000596:Amino Acids; D053304:Apolipoprotein C-II; D001056:Apolipoproteins C; D010713:Phosphatidylcholines; D014304:Triolein; D010741:Phospholipases A; D054466:Phospholipases A1; D008071:Lipoprotein Lipase