THEORY OF LIPID BILAYER PHASE-TRANSITIONS AS DETECTED BY FLUORESCENT-PROBES

We present a quantitative theory that relates the fluorescence intensity vs. temperature (I vs. T) profile of a fluorescent-labeled two-component lipid bilayer to the phase diagram of the bilayer and the partition coefficient K of the fluorophore between fluid and solid phases of the bilayer. We show how the theory can be used to evaluate K from experimental I vs. T profiles and the appropriate phase diagrams as well as to understand the different shapes of I vs. T profiles obtained with particular fluorophores and phase diagrams. Using calculated I vs. T graphs, we discuss the meaning of parameters, such as midpoint of the phase transition and onset and termination of a transition, which are often used to characterize phase transitions on the basis of fluorescence intensity vs. temperature profiles. © 1979 Springer-Verlag New York Inc.