Abstract
Endothelial lipase (EL) is a newly identified member of the triglyceride lipase gene family that hydrolyzes high-density lipoprotein (HDL) phospholipids. This study investigates the ability of the major apolipoproteins of rHDL to regulate the kinetics of EL-mediated phospholipid hydrolysis in well-characterized, homogeneous preparations of spherical rHDL. The rHDL contained either apoA-I as the only apolipoprotein, (A-I)rHDL, apoA-II as the only apolipoprotein, (A-II)rHDL, or apoA-I as well as apoA-II, (A-I/A-II)rHDL. The rHDL were comparable in terms of size and lipid composition and contained cholesteryl esters (CE) as their sole core lipid. Phospholipid hydrolysis was quantitated as the mass of nonesterified fatty acids (NEFA) released from the rHDL during incubation with EL. The V(max) of phospholipid hydrolysis for (A-I/A-II)rHDL [391.9 +/- 12.9 nmol of NEFA formed (mL of EL)(-1) h(-1)] was greater than (A-I)rHDL [152.8 +/- 4.7 nmol of NEFA formed (mL of EL)(-1) h(-1)]. The energy of activation (E(a)) for the hydrolysis reactions was calculated to be 52.1 and 34.8 kJ mol(-1) for (A-I)rHDL and (A-I/A-II)rHDL, respectively. Minimal phospholipid hydrolysis was observed for the (A-II)rHDL. Kinetic analysis showed that EL has a...Continue Reading
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