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

ion diffusion, as the energy required to move a hydrated ion through it, is extremely
high (for a monovalent ion with 2 Å radius, it takes about 40 Kcal/mol to transfer it into
the membrane core – Gennis, 1989).
Figure I.1 – a) Electron micrograph of a section from the plasma membrane of a erythrocyte membrane.
b) Schematic depiction of a lamellar arrangement of a lipid bilayer. Polar headgroups face outwards and
shield the interior hydrophobic tails (from Lodish et al., 2000).
The bilayer can be regarded as a two-dimensional solvent that provides the
hydrophobic anchor to membrane proteins in biomembranes. This two-dimensional
fluid character of the lipid bilayer is central to lipid-lipid, lipid-protein and proteinprotein
interactions. It is responsible for an increase of the efficiency of membranebound
enzymes whose substrates are located in the plane of the bilayer. The average
time for a reactant to reach a target site depends drastically on the dimensionality.
Reactions that require collisions of three bodies are very rare in three dimensions, but
can be very effective in two dimensions (Hardt, 1979; Sackmann, 1995).
The biomembrane is not only a physical barrier between the inside and outside of
the cell or between intracellular compartments and the cytosol. As the cell needs to get
nutrients in and out, the membrane must accommodate this. Some membrane-bound
2