Thermotropic Phase Behavior of Binary Bilayer Membrane of Dipalmitoylphosphatidylcholine and Ergosterol

We investigated the phase behavior of a binary bilayer membrane of dipalmitoylphosphatidylcholine (DPPC) and ergosterol, using Prodan fluorescence spectroscopy and differential scanning calorimetry to construct a temperature–composition phase diagram. We found that several important features of the phase diagram can be explained by the superlattice view, on the basis of the hexagonal lattice, which suggests the presence of a molecular cluster composed of an ergosterol molecule and its six surrounding DPPC molecules above an ergosterol composition of ca. 0.15.