Binary Mixtures of Phospholipids and Cholesterol Studied by Dynamic Heat Capacity Measurements

Abstract

Mixtures of cholesterol-dimyristoylphosphatidylcholine (DMPC) and cholesterol-dipalmitoylphosphatidylcholine (DPPC) in bilayers were investigated by 0.75 Hz ac calorimetry. DMPC with 0 to 30 mol% cholesterol and DPPC with 0 to 70 mol% cholesterol were studied over a temperature range 275–340 K. The results by ac calorimetry indicate that the mixtures of phospholipids and cholesterol have a basic structure in which 20 mol% cholesterol is intercalated: in the DMPC-cholesterol mixtures this structure is stabilized and on the other hand, in the DPPC mixtures a loose structure based on that of 20 mol% cholesterol takes place and much cholesterol-rich regions are allowed.