Electrochemistry of Biomimetic Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 252

Figure 24. Oxidative branches (baseline-corrected) of the cyclic voltammograms of
COX with the his tag attached to subunit II in the absence of oxygen, at scan rates
between 1 and 600 V s -1 (current densities normalized by the scan rate, # 1 V s -1 ).
Proceeding downwards, the scan rate increases in the order: 1, 3, 7.5, 20, 40, 300,
400, 500, and 600 V s -1 . Inset: Example of a deconvolution into four Gaussian
components. (Reprinted from Ref. 239 with kind permission from Elsevier.)
Strong evidence that the electron transfer observed by cyclic
voltammetry takes place directly within the enzyme was derived
from Soret band excited surface-enhanced resonance Raman spec-
troscopy (SERRS) taken as a function of potential. 240,241 The cyclic
voltammogram of COX oriented with the cytochrome c binding
side directed toward the electrode was used to determine the func-
tional activity of the enzyme as a function of its surface density. 242
This density was varied by diluting the thiol functionalized with
the chelator nitrilotriacetic (NTA) moiety with a non-
functionalized thiol that did not bind to the enzyme. At low COX
surface densities, the bilayer does not effectively form, and protein
aggregates are observed; on the other hand, at very high surface
densities, very little lipid is able to intrude between the closely
packed protein molecules. In both cases, redox activity is low.
Redox activity is preserved in the biomimetic membrane only at