The Membrane as a Transporter, Ion Channels and Membrane Pumps - Membrane Biophysics, Biological and Medical Physics, Biomedical Engineering - page 62

Fig. 4.8 Electrical conductance states that determine the membrane's transport properties induced
by defects. Gramicidin S (GS) induced ion conductance events in zwitterionic phosphatidyl-
choline/n-decane bilayers with 1.0 M NaCl, pH 7.0 on both sides. In ( a )and( b ) show long-time
(11 s) and short time (1 s) current traces of GS-induced ion conductance events, respectively. In
( c ) shows all point conductance level histograms constructed from the long time traces ( a ). Two
peaks in ( c ) at 0 pA/mV and around 1 pA/mV, respectively, represent the baseline conductance of
the “unperturbed” bilayer and the conductance levels of the GS-induced ion conductance events.
Additional details of the GS effects can be found in [ 9 ]
membrane effects of peptides are also highly dependent on the environment in the
peptide pathway (see Fig. 4.9 ). The properties of peptides such as water solubility,
the diffusion coefficient across the hydrophilic/hydrophobic boundaries, and, above
all, the energetics in the membrane interface are all important factors that determine
the membrane effects of peptides.
In order to generate cytolytic activity, peptides need to survive their exposure
to serum and other media, and pass through different barriers in the extracellular
matrix, the bacterial lipopolysaccharides, outer membrane regions, and/or peptido-
glycan layers [ 2 ]. After reaching the cell membrane environment, the structures
and topologies of peptides are in dynamic interchange [ 30 , 44 ]. Solid-state nuclear
magnetic resonance (NMR) spectroscopy and other biophysical techniques indi-
cate that peptide antibiotics strongly interact with lipid membranes. Bechinger's
work [ 12 , 13 ] and other studies suggest that in a bilayer environment, many pep-
tides with a higher number of amino acids in their sequences, such as cecropins,
magainins, etc., exhibit amphipathic α -helical conformations and their helix axes
become parallely aligned to the membrane surface. On the other hand, other pep-
tides such as alamethicin, gramicidin A, etc., are found to experience trans-membrane