19F-NMR and fluorescence polarization of yeast plasma membrane and isolated lipids

16-Fluoropalmitic acid was incorporated biosynthetically into the plasma membrane of yeast and the F-NMR spectra of the intact membrane and of aqueous dispersions of membrane lipids were compared. The greater degree of resonance broadening in the intact membrane reveals a lesser degree of mobility of the acyl chains. Fluorescence polarization studies with a probe that monitors the polar environment and one that detects viscosity changes in the inner core of the bilayer indicate hindered motions of the polar head groups and acyl chains in the intact membrane as compared to liposomes prepared from membrane lipids. The observations indicate that the bulk of lipids in the yeast membrane experiences immobilization by proteins and that membrane proteins influence lipid-lipid interactions and inhibit lipid phase transition.