APOLIPOPROTEIN A-II INFLUENCES THE SUBSTRATE PROPERTIES OF HUMAN HDL(2) AND HDL(3) FOR HEPATIC LIPASE

Hepatic lipase has a demonstrated dual role in plasma lipid transport in that it participates in the removal of remnants of triglyceride-ric h lipoproteins from the circulation and in the metabolism of plasma HD L. The study presented here investigated the substrate properties for hepatic lipase of HDL differing in density and apolipoprotein (ape) co mposition. Rates of fatty acid liberation were twofold higher in HDL, compared with the respective HDL, subspecies. Within each density clas s, enzyme-catalyzed fatty acid release was nearly twofold higher from HDL containing apoA-II compared with HDL devoid of apoA-II. When nativ e HDL, devoid of apoA-II was reconstituted with dimeric apoA-II in vit ro, rates of fatty acid liberation in reconstituted particles were sim ilar to those in native HDL, containing apoA-II. HDL containing apoA-I I competed more effectively with small VLDL for binding of hepatic lip ase than HDL devoid of apoA-II. HDL,, particularly apoA-II-containing HDL(5), reduced lipolysis of triglyceride and total fatty acid liberat ion in small VLDL. We conclude that the substrate properties of HDLs f or hepatic lipase are influenced by both their size and apoA-II conten t. Moreover, size as well as apoA-II content may indirectly affect rem nant clearance.