Thermotropic properties and molecular dynamics of cholesteryl ester rich very low density lipoproteins: effect of hydrophobic core on polar surface.

摘要: Cholesteryl ester rich very low density lipoproteins (CER-VLDL), isolated from the plasma of rabbits fed a hypercholesterolemic diet, have been studied by differential scanning calorimetry (DSC), 13C nuclear magnetic resonance (NMR), and spin-label electron paramagnetic (EPR) to determine temperature-dependent dynamics cholesteryl esters in hydrophobic core phospholipids on polar surface. Intact CER-VLDL exhibit two DSC heating endotherms; these occur at 40-42 45-48 degrees C. also 50.0 55.1 C correspond smectic----cholesteric cholesteric----isotropic liquid-crystalline phase transitions. A model mixture containing linoleate, oleate, palmitate ratio (0.21, 0.51, 0.28 mol fraction) similar that exhibited comparable endotherms 45.2 51.5 37 gave NMR spectra contained no resonances assignable ring carbons but detectable broad for some fatty acyl chain carbons, suggesting were state. When was heated 42 C, carbon became detectable; 48 they narrow, indicating an isotropic, liquid-like With increasing temperature over range 38-60 C3 C6 narrowed differentially. Similar spectral changes observed synthetic mixture, except occurred temperatures about 10 higher. These results indicate transitions do not directly correlate with pure esters. (5-Doxylpalmitoyl)-phosphatidylcholine (5-DP-PC) (12-doxylstearoyl)phosphatidylcholine (12-DS-PC) used probe surface monolayer CER-VLDL; corresponding (5-DP-CE 12-DS-CE) core. None probes detected abrupt change EPR order parameters, S, or maximum splitting, 2T max, 20-58 even though 12-DS-PC 5-DP-PC can detect phospholipid bilayers 12-DS-CE 5-DP-CE neat However, did much greater neutral lipids than those normal triglyceride-rich VLDL.(ABSTRACT TRUNCATED AT 400 WORDS)