Biomedical Engineering Reference
In-Depth Information
0.30
0.31
0.32
0.33
10 150000
10 150000
10 100000
10 100000
10 50000
10 50000
10 0
10 0
0.30
0.31
0.32
0.33
r
0.27
0.28
0.29
0.30
10 150000
10 150000
10 100000
10 100000
10 50000
10 50000
10 0
10 0
0.27
0.28
0.29
0.30
r
Fig. 5.16 A plot of the energy as a function of the reaction coordinate for a gA channel in lipid
bilayer energetics at different values of r LL (left
right: r LL
=
6
.
48074, 6
.
9282 ( lower panel ),
7
74597 Å ( upper panel )) for the first- (single-dashed curve) and second-(double-dashed
curve) order lipid screening. q L
.
34847, 7
.
/
q gA
=
0
.
0025
exponential growth in their instability and finally may undergo a structural transition
which has been experimentally observed (see Fig. 5.13 ). As
(
d 0
l
)
approaches 0 Å,
the drastic drop in the values of G I causes the value of U
to quickly approach
the level whose order of magnitude is comparable to that of the smaller interaction
energy level ( U gA , gA (
(
r
)
—see Eq. 5.16 ) between two gA monomers with only direct
Coulomb binding effects with the bilayer. Under this condition, the bilayer defor-
mation energy is no longer an important regulator of channel function. Figure 5.16
demonstrates that the geometry of the lipids is an important regulator, and the tran-
sition G I
r
)
G II occurs at increasing reaction coordinates with increasing values
of lipid dimension parameter r LL . Identical trends with quantitatively slightly differ-
ent energetics have been observed for Alm channels in lipid bilayers (see Figs. 5.17
and 5.18 ).
Figures 5.19 and 5.20 show how lipid charge relative to the charge of the channel-
forming peptides changes the values of both G I
and G II (see Fig. 5.19 ) and
 
 
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