title: Comparison of the triacylglycerol hydrolase activity of human post-heparin plasma lipoprotein lipase and hepatic triacylglycerol lipase. A monolayer study.
abstract: Interfacial catalysis of hepatic triacylglycerol lipase (H-TGL) and lipoprotein lipase (LpL) isolated from human post-heparin plasma was investigated with mixed monolayers of trioleoylglycerol (TO) and egg phosphatidylcholine. Rates of enzyme catalysis were dependent on surface pressure, substrate concentration, apoC-II (the activator protein for LpL), and cholesteryl oleate (CO). LpL showed a surface pressure optimum between 22 and 24 mN m-1, whereas H-TGL activity decreased at pressures greater than 20 mN m-1. LpL activity was enhanced greater than 10-fold by apoC-II; 1 M NaCl inhibited enzyme activity. ApoC-II, apoC-III, apoA-I, apoA-II, and 1 M NaCl had no effect on H-TGL activity. The substrate (TO) dependency was different for the two lipases. For LpL, there was a marked enhancement of enzyme activity between 2 and 4 mol % TO, whereas for H-TGL, enzyme activity increased linearly between 1 and 10 mol % TO. LpL activity toward monolayers containing 2 mol % TO was enhanced 2.6-fold by the addition of 5 mol % CO; cholesteryl ester had no effect on H-TGL activity. These findings suggest that the two lipolytic enzymes have different interfacial properties, which may have relevance to the rates of hydrolysis of triacylglycerols at a lipoprotein interface.
mesh_terms: D006493:Heparin; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008049:Lipase / Q000378:metabolism*; D008071:Lipoprotein Lipase / Q000097:blood*; D008081:Liposomes; D008099:Liver / Q000201:enzymology*; D011312:Pressure; D013499:Surface Properties
chemical_list: D008081:Liposomes; D006493:Heparin; D008049:Lipase; D008071:Lipoprotein Lipase