Evidence that apolipoprotein A-I facilitates hepatic lipase-mediated phospholipid hydrolysis in reconstituted HDL containing apolipoprotein A-II.
This study examines hepatic lipase (HL) mediated phospholipid hydrolysis in mixtures of apolipoprotein-specific, spherical reconstituted high-density lipoproteins (rHDL). We have shown previously that apolipoprotein A-I (apoA-I) and apoA-II have a major influence on the kinetics of HL-mediated phospholipid and triacylglycerol hydrolysis in well-characterized, homogeneous preparations of spherical rHDL [Hime, N. J., Barter, P. J., and Rye, K.-A. (1998) J. Biol. Chem. 273, 27191-27198]. In the present study, phospholipid hydrolysis was assessed in mixtures of rHDL containing either apoA-I only, (A-I)rHDL, apoA-II only, (A-II)rHDL, or both apoA-I and apoA-II, (A-I/A-II)rHDL. The rHDL contained trace amounts of radiolabeled phospholipid, and hydrolysis was measured as the formation of radiolabeled nonesterified fatty acids (NEFA). As predicted from our previous kinetic studies, the (A-II)rHDL acted as competitive inhibitors of HL-mediated phospholipid hydrolysis in (A-I)rHDL. Less expected was the observation that the rate of phospholipid hydrolysis in (A-II)rHDL was enhanced when (A-I)rHDL were also present in the incubation mixture. The rate of phospholipid hydrolysis in (A-I/A-II)rHDL was also greater than in (A-II)rHDL, indicating that apoA-I enhances phospholipid hydrolysis when it is present as a component of (A-I/A-II)rHDL. It is concluded that apoA-I enhances HL-mediated phospholipid hydrolysis in apoA-II containing rHDL, irrespective of whether the apoA-I is present in the same particle as the apoA-II [as in (A-I/A-II)rHDL] or whether it is present as a component of a different particle, such as when (A-I)rHDL are added to incubations of (A-II)rHDL.
Hime
N J
NJ
Department of Medicine, Royal Adelaide Hospital, University of Adelaide, South Australia, Australia.
Barter
P J
PJ
Rye
K A
KA
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000378:metabolism; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000378:metabolism*; D016633:Apolipoprotein A-II / Q000737:chemistry / Q000378:metabolism*; D001667:Binding, Competitive; D002250:Carbon Radioisotopes / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007700:Kinetics; D008049:Lipase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008823:Micelles; D010713:Phosphatidylcholines / Q000378:metabolism; D010743:Phospholipids / Q000037:antagonists & inhibitors / Q000378:metabolism*
D016632:Apolipoprotein A-I; D016633:Apolipoprotein A-II; D002250:Carbon Radioisotopes; D004791:Enzyme Inhibitors; D008075:Lipoproteins, HDL; D008823:Micelles; D010713:Phosphatidylcholines; D010743:Phospholipids; D015060:1,2-Dipalmitoylphosphatidylcholine; D002784:Cholesterol; D008049:Lipase; C028694:1-palmitoyl-2-oleoylphosphatidylcholine