Biomedical Engineering Reference
In-Depth Information
moderate surface coverages, in which a continuous lipid bilayer is
present and the protein molecules are not forced to aggregate.
In the presence of oxygen, electrons transferred from the elec-
trode to the redox centers of COX are irreversibly transferred to
oxygen, leading to a notable increase of the reduction peak, which
now lies at -202 mV/NHE, and to a continuous electron transfer.
The cyclic voltammogram also shows a further reduction peak at
422 mV/NHE. This is due to the catalytic turnover of COX,
which reduces oxygen to water and pumps protons into the inter-
stitial space between the electrode and the lipid bilayer. Proton
electroreduction at the electrode surface determines the second
reduction peak. The absence of direct electron transfer and of pro-
ton electroreduction when COX is oriented with the cytochrome c
binding site turned toward the solution confirms the orientation
dependence both of direct electron transfer and of transmembrane
proton transport.
VI. CONCLUSIONS
The use of electrochemical techniques such as cyclic voltammetry,
EIS and charge transient recordings for the investigation of biolog-
ical systems is becoming increasingly popular, just as the applica-
tion of the concepts of electrochemical kinetics and of the structure
of electrified interfaces to the interpretation of the electrochemical
response.
Several efforts are presently made to realize biomembrane
models consisting of a lipid bilayer anchored to a solid electrode
through a hydrophilic spacer and satisfying those requirements of
ruggedness, fluidity and high electrical resistance that are neces-
sary for the incorporation of integral proteins in a functionally ac-
tive state. A unique feature of these biomembrane models is the
achievement of the maximum possible vicinity of a functionally
active integral protein to an electrode surface (the electrical trans-
ducer). The capacitive currents resulting from the activation of ion
pumps, transporters, channel proteins and channel-forming pep-
tides incorporated in these biomembrane models can be analyzed
over a broad potential range by electrochemical techniques, which
are by far less expensive than other techniques presently adopted.
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