Magnification of Shape Fluctuations

Manneville, Jan-Baptiste, Magnification of Shape Fluctuations of Active Giant Unilamellar Vesicles, 6, 351. 

From the point of view of non-equilibrium statistical physics, understanding the behavior of such active membranes is challenging. Recent theoretical results [8,9] have shown that the shape fluctuations of active membranes should differ both qualitatively and quantitatively from those of passive membranes. The presence of active proteins imbedded in the membrane is expected to induce a magnification of shape fluctuations due to a modification of the fluctuation spectrum. In search of the simplest model to test the theory [8,9], the shape fluctuations of giant lipid vesicles have been studied with the active protein, bacteriorhodopsin (BR) incorporated inside the lipid bilayer. 

G(t) decays with correlation time because the fluctuation is more and more uncorrelated as the temporal separation increases. The rate and shape of the temporal decay of G(t) depend on the transport and/or kinetic processes that are responsible for fluctuations in fluorescence intensity. Analysis of G(z) thus yields information on translational diffusion, flow, rotational mobility and chemical kinetics. When translational diffusion is the cause of the fluctuations, the phenomenon depends on the excitation volume, which in turn depends on the objective magnification. The larger the volume, the longer the diffusion time, i.e. the residence time of the fluorophore in the excitation volume. On the contrary, the fluctuations are not volume-dependent in the case of chemical processes or rotational diffusion (Figure 11.10). Chemical reactions can be studied only when the involved fluorescent species have different fluorescence quantum yields. 

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