PARTITION OF A FLUORESCENT MOLECULE BETWEEN LIQUID-CRYSTALLINE AND CRYSTALLINE REGIONS OF MEMBRANES

We have determined the partition coefficient of the fluorescent molecule perylene between liquid crystalline and crystalline regions of vesicle membranes formed from binary mixtures of several lipids. We measured the fluorescence intensity of perylene in these vesicles as a function of temperature and used the intensity profiles, together with a theory developed in a previous paper, to determine the partition coefficient defined as the ratio of the concentration of perylene in the liquid-crystalline (fluid) regions of the membrane to the concentration in the crystalline (solid) phase. In vesicles composed of dipalmitoyl phosphatidylcholine/distearoyl phosphatidylcholine (dppc/dspc) mixtures and of dipalmitoyl phosphatidylcholine/dipalmitoyl phosphatidylethanolamine (dppc/dppe) mixtures, the partition coefficient is close to unity. Its value is 1.04±0.18 for dppc/dsp mixtures and 1.10±0.26 for dppc/dppe mixtures. In vesicles composed of dimyristoyl phosphatidylcholine/distearoyl phosphatidylcholine mixtures, the partition coefficient was more difficult to determine and its value ranged from 0.3 to 7. © 1979 Springer-Verlag New York Inc.