title: Reassembled plasma low density lipoproteins. Phospholipid-cholesterol ester-apoprotein B complexes.
abstract: Reassembled low density lipoprotein (LDL) complexes have been prepared by the interaction of lipid-free sodium deoxycholate-solubilized apoprotein B (apoB) of native human LDL with preformed, 200 A in diameter, microemulsions of cholesteryl oleate (CO), surface-stabilized by either egg yolk phosphatidylcholine ( EYPC ) or dimyristoyl phosphatidylcholine (DMPC). Gel chromatography of PC/CO/apoB complexes shows co-elution of the complex at 43% PC, 43% CO, and 14% apoB. Negative stain electron microscopy shows the particles to be circular, homogeneous, and approximately 200 A in diameter. PC/CO/apoB complexes exhibit beta-migration on agarose gels and show one high molecular weight protein band on 3.0% sodium dodecyl sulfate-polyacrylamide gels. Differential scanning calorimetry and x-ray scattering show the lipids in the complexes to undergo at least two specific thermal transitions depending on lipid composition, one associated with the core-located cholesterol esters similar to LDL and the protein-free microemulsions and the other from the phospholipid forming the surface monolayer. In addition, particle disruption-protein unfolding/denaturation occur irreversibly at 80-85 degrees C. At 4 degrees C, the secondary structure of apoB on complexes of EYPC /CO/apoB is similar to that of native LDL. For complexes of DMPC/CO/apoB, the secondary structure shows less alpha-helix which correlates with the difference in surface lipid environment. The reassembled complexes of PC/CO/apoB provide a defined system in which the components may be varied systematically in order to study the molecular organization, molecular interactions, and metabolism of LDL.
mesh_terms: D001053:Apolipoproteins / Q000097:blood* / Q000302:isolation & purification; D001055:Apolipoproteins B; D002152:Calorimetry, Differential Scanning; D002788:Cholesterol Esters / Q000097:blood*; D004591:Electrophoresis, Polyacrylamide Gel; D004655:Emulsions; D006801:Humans; D008077:Lipoproteins, LDL / Q000097:blood*; D008854:Microscopy, Electron; D010743:Phospholipids / Q000097:blood*
chemical_list: D001053:Apolipoproteins; D001055:Apolipoproteins B; D002788:Cholesterol Esters; D004655:Emulsions; D008077:Lipoproteins, LDL; D010743:Phospholipids