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Biophysical studies of membrane proteins/peptides. Interaction with ...

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in the L α phase, while lateral diffusion in the plane <strong>of</strong> the bilayer and freedom <strong>of</strong><br />

rotation remains high.<br />

Figure I.5 – A – Differential scanning calorimetry pr<strong>of</strong>ile <strong>of</strong> DMPC, 1,2-dimyristoyl-sn-glycero-3-<br />

phosphatidylethanolamine (DMPE), and 1,2-dimyristoyl-sn-glycero-3-phosphatidic acid (DMPA). B –<br />

Depiction <strong>of</strong> most common lamellar lipid phases: the fluid L α phase, the gel L β and the ripple P β’ phase<br />

(taken from Gennis, 1989).<br />

1.6. Membrane thickness<br />

Due to the complex chemical structure <strong>of</strong> lipids, the chemical environment along the<br />

normal axis <strong>of</strong> the bilayer is highly stratified. In hydrated bilayers, fluctuations add<br />

increased complexity to the task <strong>of</strong> the structural description <strong>of</strong> the lipid <strong>membrane</strong>. A<br />

description for the position <strong>of</strong> the atoms inside the bilayer using a broad statistical<br />

distribution function can be used. Figure I.6 is a representation <strong>of</strong> the liquidcrystallographic<br />

structure <strong>of</strong> L α -phase dioleoyl-sn-glycero-3-phosphatidylcholine<br />

(DOPC) bilayers along the axis <strong>of</strong> the bilayer normal.<br />

In the presence <strong>of</strong> this dynamical concept for the lipid bilayer structure it becomes<br />

difficult to define certain bilayer properties such as <strong>membrane</strong> thickness. It is reasonable<br />

nevertheless to assume the bilayer thickness as equal to the distance between the peaks<br />

12

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