Phase Diagrams of 3-Component Domain-Forming Membrane Model Systems

Gerald W. Feigenson, Professor, Department of Molecular Biology & Genetics, Director of Graduate Studies, Field of Biophysics, 201 Biotechnology Building, Cornell University, Ithaca, NY 14853

The phase behavior of chemically well-defined multi-component lipid mixtures can provide a basis for understanding compositional domains in natural biomembranes. However, for mixtures as complex as 3 components, no correct phase diagram has yet been published. We chose DPPC/DLPC/cholesterol as the 3-component mixture most amenable to complete analysis. We have used a number of different methods in order to (1) correctly identify all of the different regions; and (2) establish precise phase boundaries. For phase identification, x-ray diffraction, electron spin resonance, fluorescence correlation spectroscopy, and fluorescence imaging have been useful. For phase boundary determination, different methods are more effective. The most useful of these has been composition dependence of the fluorescence of probes at high dilution.

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