Biomedical Engineering Reference
In-Depth Information
O
O
O
O
O
O
O
O
O
O
O
O
O
OO
O
O
O
O
c 0
c 1
c 2
O
O
O
O
O
current position
O
O
previous position
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OO
O
O
O
O
O
O
O
O
c 0
O
O
c 1
c 2
O
O
O
O
O
channel forming monomers
monomers in the vicinity
Fig. 5.10 2D view of the channels only, from the membrane surface (where alamethicin monomers
are seen only along their longitudinal direction so they appear as circles) represent the two possible
mechanisms of inter-channel conduction level transformations. In the bottom panel, we assume
that the monomers already exist in a structured form of the alamethicin channel where the pore
radius changes by reorganization of the channel forming monomers. The other 2D view illustrates a
possible model of alamethicin channel formation, and a transformation between different conduction
levels where the pore radius increases by addition of monomers from the surrounding space where
monomers randomly move into the channel. The reduction in the pore radius occurs by releasing
the monomers from the cylindrical surface of the channels. Both of the models in 2D views are valid
explanations of the upper 3D structures of alamethicin channels (Figures 5.8 and 5.9 ). Taking three
monomers in the zeroth conductance level is an arbitrary choice but the reverse calculation using
experimental values of cylindrical alamethicin pore conductances and the theoretical values of the
cross-sectional areas of different alamethicin pores hint that three monomers may form the zeroth
conductance level. Faded circles and bonds in 2D views are shown to distinguish their inactivity in
the channel's conduction mechanism
gramicidin A channels experience only monomer state
dimer state transitions,
so the channel functions do not require overly complicated analyses, but mainly the
understanding of the channel stability. We have addressed this sufficiently so far
for the two distinguishable gramicidin A energy states corresponding to the dimer
and monomer states. However, if gramicidin A states present a continuum distribu-
tion of local energy traps, the gramicidin A channel's phenomena require a unique
theoretical treatment. We briefly address this here. Due to structural complexity,
alamethicin channels, and some other complex channels require complicated phe-
nomenological models to completely explain the channel energetics. Specifically,
the transitions between different channel conformations and associated independent
and transition probabilities need to be clearly understood. Alamethicin channels'
 
 
Search WWH ::




Custom Search