Membrane Fluidity and Diffusive Transport
The fluid mosaic model (Singer and Nicolson, 1972) provides not only a picture of the basic structure of membranes but also implies certain dynamic characteristics of its components. Thus the lipids of the bilayer are subject to Brownian motion which endows them with rotational and translational mobility. The same is true of those proteins which are not attached to the cytoskeleton, although their mobility is much smaller. In the last few years, considerable effort has gone into the measurement of the rotational and translational mobilities of both lipid analogue probes and of membrane proteins, in model systems, as well as in biological membranes. It has become clear that the lateral mobility of membrane components not only provides an interesting demonstration of the fluidity of a two-dimensional liquid, but that it plays an important role in various functions of the cell membrane. For example, membrane receptors are known to migrate and aggregate in certain small regions of the membrane (coated pits), and the electron transport between cytochromes in the mitochondrial membrane appears to be diffusion-limited (Hackenbrock et al., 1986). These and other cellular functions related to the lateral mobility of membrane components have recently been reviewed by Axelrod (1983).
KeywordsLateral Diffusion Diffusive Transport Outer Leaflet Lateral Mobility Excimer Formation
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