Fluorescence Polarization Studies of Membrane Fluidity: Where Do We Go from Here?
In the most general terms, the concept of membrane fluidity comprises a number of the motional characteristics of membrane components. It includes the translational and rotational motions of proteins and the translational diffusion of lipids in the plane of the membrane (“mobility”), and the segmental motions of lipid acyl chains and the reorientational motions of lipid polar head groups (“fluidity”). Fluidity appears to be an essential element of membrane structure and it is intimately related to biological function. Modifications in the composition of membrane lipids often result in alterations in membrane function. In numerous experiments (which are not considered explicitly in this review) it has been possible to detect the alteration in the physical properties of the membrane lipids and thus to link the alteration in the membrane composition and its structure to its function. For the purposes of this review we will regard fluidity as arising from the disordered nature of the lipid bilayer and mobility as reflecting diffusion of molecules within the matrix. While fluidity is a prerequisite for mobility, additional cellular factors may ultimately limit or determine the mobility of membrane proteins.
KeywordsAcyl Chain Fluorescence Lifetime Resonance Energy Transfer Probe Molecule Fluorescence Polarization
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