| Abstract: | 1H NMR spectroscopy at 200 MHz was used to study triglyceride crystalline leads to liquid transitions which occurred on heating between 10 and 50 degrees C in very low density lipoprotein and subfractionated chylomicron particles from nonhuman primates fed a saturated fat (butter fat) diet. Model system studies of pure triglycerides (triolein, tripalmitin and a 1:1 mixture) and emulsion particles consisting of these triglycerides with a surface of egg phosphatidylcholine showed that high resolution spectra were obtained only from liquid triglycerides. In lipoprotein spectra, changes in 1H NMR peak intensities and line widths accompanied the solid leads to liquid transition of the constituent triglycerides. Peak areas of fatty acyl resonances were proportional to the percentage of melted triglyceride determined by differential scanning calorimetry. NMR peak area measurements showed that the calorimetric transition involved the melting of relatively greater numbers of saturated fatty acyl chains than unsaturated chains; at temperatures well below the solid leads to liquid transition, the lipoproteins contained a significant fraction (approximately 33%) of liquid triglycerides which were relatively enriched in unsaturated fatty acyl chains. For model systems containing mixtures of solid and liquid triglycerides, the temperature dependence of line widths of fatty acyl resonances demonstrated that solid triglycerides decreased the mobility of the liquid triglycerides. A similar temperature dependence for the lipoprotein resonances suggested that solid and liquid species are co-mixed in individual lipoprotein particles within a purified subfraction. Temperature-dependent line width and intensity changes were observed for the phospholipid-choline methyl resonance in lipoprotein spectra and were apparently independent of the core transition. |
