Phase Heterogeneity in Cholesterol-containing Ternary Phospholipid Lamellar Phases

Pseudo-ternary mixtures of lamellar phase phospholipids (DPPC and brain sphingomyelin with cholesterol) were studied below Tm, while comparing the influence of cholesterol content, temperature and the presence of small quantities of Vitamin D binding protein (DBP) or Vitamin D receptor (VDR). The measurements, conducted by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR), cover a range of cholesterol concentrations (20% mol. wt to 40% mol. wt.) and physiologically relevant temperature range (294 K - 314 K). In addition to rich intra-phase behaviour, data and modelling are used to approximate the lipids headgroup location variations under the above-mentioned experimental conditions.