Interaction of human plasma lecithin:cholesterol acyltransferase and venom phospholipase A2 with apolipoprotein A-I recombinants containing nonhydrolyzable diether phosphatidylcholines.
Partially reassembled high density lipoproteins (R-HDL) composed of apolipoprotein A-I and nonhydrolyzable analogues of phosphatidylcholine have been prepared, and their physical properties and reactivities as substrates for lecithin: cholesterol acyltransferase and three phospholipases were tested. The stereo-chemical pairs L-DMPC-ether (1,2-O-ditetradecyl-sn-glycero-3-phosphorylcholine) and D-DMPC-ether (2,3-O-ditetradecyl-sn-glycero-1-phosphoryline) or L-DMPC (1,2-dimyristoyl-sn-glycero-3-phosphoryl-choline) and D-DMPC (2,3-dimyristoyl-sn-glycero-1-phosphorylcholine) have similar thermal properties. R-HDL composed of these four lipids also have similar thermal properties as well as lipid/protein ratios, molecular weights, and protein conformations. Vmax and apparent Km values for lecithin: cholesterol acyltransferase on R-HDL consisting of linear combinations of L-DMPC and D-DMPC, L-DMPC-ether, or D-DMPC-ether plus 6 mol % cholesterol were measured. For the ether lecithins, there was a linear increase in Vmax with percentage of the acyl donor, L-DMPC, in R-HDL; over the same range, there was no change in Km. A comparison with bee venom and Naja melanoleuca phospholipase A2 demonstrated that the venom enzymes have turnover numbers almost 3 orders of magnitude greater than has lecithin:cholesterol acyltransferase; the activity of the phospholipases was profoundly affected by the physical state of the lipid, whereas lecithin: cholesterol acyltransferase activity was not. The differences between these two types of enzymes, which cleave the same bonds of a phosphatidylcholine, are assigned to different catalytic mechanisms. These studies show that R-HDL containing sn-glycero-3-phosphorylcholines and sn-glycero-3-phosphorylcholine ethers have similar structure, properties, and affinities for phospholipolytic enzymes.
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000032:analysis*; D001514:Bee Venoms / Q000032:analysis*; D004546:Elapid Venoms / Q000032:analysis*; D006358:Hot Temperature; D006801:Humans; D007700:Kinetics; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood*; D010713:Phosphatidylcholines / Q000032:analysis*; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D001514:Bee Venoms; D004546:Elapid Venoms; D010713:Phosphatidylcholines; D007862:Phosphatidylcholine-Sterol O-Acyltransferase; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2