Role of membrane heterogeneity in interaction with molecules
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This chapter provides an overview of lipid-bilayer membranes. The lipid bilayers sustain a substantial dynamic heterogeneity. This dynamic heterogeneity is a consequence of the fact that the membrane molecular assembly is a many-particle system sustaining strong lateral density and compositional fluctuations. The heterogeneity of the membrane varies with temperature and acyl-chain length of the phospholipid molecules in the membrane, as well as the mixing properties of the lipid species constituting the lipid-bilayer. The foreign molecules interacting with the lipid membrane have a strong influence on the lateral density and compositional fluctuations and the associated dynamic heterogeneity of the lipid membrane state. Macroscopically, the dynamic membrane heterogeneity is manifested in enhanced response functions, such as specific heat, and an enhancement of the passive membrane permeability. The hypothesis put forward is that dynamic lipid-bilayer heterogeneity accompanied by the formation of lipid domains and their associated network of interfacial regions in the membrane plane support important membrane functions. This hypothesis is supported by the close correlation found among the calculated interface formation from lipid-bilayer model simulations and the experimentally measured passive permeability functions and the rate of activation of enzymes such as phospholipases.