Biomedical Engineering Reference
In-Depth Information
Vesicle unrolling was facilitated by using a gold-supported
monolayer consisting of a mixture of short-chain polyethyleneoxy-
thiol hydrophilic spacers and of thiolipid molecules consisting of
the same spacer covalently bound to a cholesteryl group. 13 These
cholesterol derivatives serve as anchoring units that penetrate into
the outer monolayer of unilamellar vesicles and increase both the
fluidity of gel-phase bilayers and the rigidity of liquid-crystalline-
phase bilayers. Vesicle fusion on monolayers of mixtures of these
colesteryl-based thiolipids and spacers takes place only for frac-
tional surface coverages of the thiolipid exceeding a minimum
value. In situ investigation of these tBLMs by ATR-FTIR spec-
troscopy indicates that the distal leaflet of these tBLMs is com-
prised of pure lipid and the proximal one is comprised of a mixture
of cholesteryl and lipid. 205 A particular tBLM was fabricated by
anchoring to a smooth template-stripped gold surface a mixture of
DPTL and of a spacer (TEGL) in which the two phytanyl chains of
the DPTL molecules were replaced by a terminal hydroxyl group
(see Fig. 1 ); 27 a lipid bilayer was then formed on top of this mix-
ture by vesicle fusion. Contact mode and friction mode AFM im-
ages of the mixed DPTL-TEGL monolayer seem to exclude phase
segregation. Ion-channel activity of gramicidin and melittin incor-
porated in this tBLM and ion selectivity of gramicidin were veri-
fied by EIS.
A gold-supported mixture of a triethyleneoxythiol covalently
linked to a cholesteryl group, with a lipid monolayer on top, and of
6-mercaptohexanol, with a lipid bilayer on top, was used to incor-
porate cytochrome bo3 ( cbo3 ). 4 This is the primary membrane-
bound terminal oxidase of Escherichia coli , which catalyzes the
oxidation of ubiquinol-8 and the reduction of oxygen to water in a
process coupled to proton translocation across the cell membrane.
Upon incorporating bo3 and ubiquinone-8 into this tBLM in the
presence of oxygen, a reduction cyclic voltammogram was record-
ed at potentials negative enough to cause ubiquinone-8 electrore-
duction to ubiquinol-8 on gold. In this way, ubiquinol-8 transfers
electrons continuously from the gold electrode to cbo3 , where it is
reoxidized by oxygen to ubiquinone-8, which moves back to the
electrode surface. The height of the sigmoidal-shaped catalytic
cyclic voltammograms increased with an increase in oxygen con-
centration, whereas it was completely suppressed upon addition of
1 mM cyanide ion.
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