Investigation on One Liquid to Two Liquid Transition in Lipid Membranes( I )

It is widely accepted that lipid domains with differing lipid/protein compositions, physical properties, and function exist in the membranes. Among them, the domains (lipid rafts) enriched in cholesterol and sphingolipid have been implicated to play important roles in a wide range of biological processes. Investigation of model membranes containing ternary mixtures of unsaturated phospholipid, saturated phospholipid, and sterol have been performed on various systems in order to understand the interactions governing the raft formation. One intriguing result is that while POPC/DPPC/cholesterol membranes display only one liquid phase, POPC/DPPC/ergosterol membranes display coexistence of lo and ld phases for a given temperature. Here we propose to study model membranes POPC/DPPC/(cholesterol_1-x ergosterol_x). By replacing cholesterol with ergosterol, we attempt to observe the evolution from one liquid to two liquid by varying the sterol composition. We will also study (POPC_1-x DOPC_x) /DPPC/cholesterol model membranes, which also exhibit one liquid (x=0) to two liquid transition (x=1) transition. We will explore the phase behavior between x=0 and x=1 region. In both cases, the temperature-composition phase diagrams will be established.