FIGURE 4.

Model for the two-dimensional micellelike microheterogeneous structure proposed for a POPC-Chol membrane formed at low cholesterol concentrations. Cholesterol is represented by a solid ellipse, while POPC is represented by the ellipse with a gradient ranging from dark (representing the fully saturated palmitoyl chain of POPC) to light (representing the cis-unsaturated oleoyl chain of POPC). The preferential solvation of the (flat and rigid) cholesterol molecule by the fully saturated chains of POPC orients this side of the POPC molecules toward the cholesterol molecule while the cis-unsaturated chains are oriented away from it forming a two-dimensional micellelike structure.