Biomedical Engineering Reference
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Figure 15. Conductance change ǻ
G
of a pore-spanning membrane during the expo-
sure to gramicidin-doped (2 mol%) DOPC LUVs (Ɣ) and gramicidin-free DOPC
LUVs (ż). Buffer: 10 mM TRIS, 100 mM TMA, 10 mM KCl, pH 8.6.
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It can be concluded that a transfer of conducting gramicidin
dimers takes place upon incubation of liposomes with a pore-
suspending membrane. We suggest that the transfer process is
driven by fusion of vesicles with the pore-suspending membrane
based on the following facts: It is known that gramicidin, once in-
corporated into a lipid bilayer, does not readily exchange to anoth-
er bilayer,
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i.e., there is no partition of gramicidin between the
aqueous and the membrane phase as is known for ion carriers such
as valinomycin.
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Moreover, gramicidin only forms conducting
dimers if the peptide is transferred to both leaflets of the bilayer.
Since we monitor the conducting transmembrane channels by im-
pedance spectroscopy (monomers in only one leaflet are not con-
ducting), it appears likely that gramicidin is transferred to the pore-
suspending bilayers via fusion of the peptide-doped liposomes re-
sulting in gramicidin in both leaflets. The study also reveals that
the process of fusion takes several hours. This is a drawback when
working with transmembrane proteins, which are prone to fast in-
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