Proteins electrodes

E. Topoglidis, T. Lutz, R.L. Willis, CJ. Barnett, A.E.G. Cass, and J.R. Durrant, Protein adsorption on nanoporous Ti02 films a novel approach to studying photoinduced protein/electrode transfer reactions. Faraday Discuss. 116, 35—46 (2000). 

Fe "-OOH (ES) complex, 43 95-97 heme-bound CO, 43 115 lock-and-key model, 43 106-107 mutation in proximal heme cavity, 43 98 residue location, 43 101-102 van der Waals surfaces, 43 112-113 Velcro model, 43 107 zinc-substituted, 43 110-111 plastocyanin, cross-linked, cyclic voltammogram, 36 357-358 promoters, 36 345-346 protein-electrode complex, 36 345, 347 redox potential, 36 349 self-exchange rate constants, 36 402 stability at electrode/electrolyle interface, 36 349-350... 

The electron transfer in biology usually involves initial protein-protein complex formation based on the complementarity of the docking sites. Efficient protein-electrode reactions appear to have some similarities to the way in which proteins act with their natural redox partner [22]. Therefore, methods for chemically modifying electrode surfaces as to mimic the biological situation were developed. The heterogeneous electron transfer between proteins and electrodes may be coupled with other reactions where the proteins act as vectorial mediators [25,26]. 

The Marcus Theory can also be applied for heterogeneous electron transfer reaction at electrode surfaces [24 and references therein]. The electronic coupling between the protein and the electrode can be varied using different self-assembled monolayers controlling the orientation of the redox active protein on the surface and the distance between the redox active site of the protein and the electrode. The driving force is related to the appHed potential and the redox potential of the protein. In many cases the rate of electron transfer across the protein-electrode interface is limited by conformational reorganization. This has focussed the efforts of many groups on tailored interaction between proteins and enzymes and electrode surfaces. 

A more detailed kinetic investigation of the Au/Bipy/cytochrome c system was carried out using the rotating ring-disk technique (12). It was found that rate constants for adsorption and desorption of the protein were 3 x cm sec" and 50 sec", respectively. The limiting first-order rate constant within the protein-electrode complex was determined as 50 sec", a reasonable value as compared to that of long-range electron transfer between or within proteins. 

These results support the electrode reaction mechanism originally proposed by Hill et al. (17), i.e., hydrogen bonding between the lysine residues surrounding the exposed heme edge of cytochrome c and the pyridyl nitrogens at the electrode surface stabilizes a transient protein-electrode complex oriented so as to allow rapid electron transfer to and from the heme group. 

Armstrong, F.A. and Brown, K.J. (1987) Studies of protein-electrode interactions by organosilyl derivatisation of pyrolytic graphite electrodes. Journal of Electroanalytical Chemistry, 219, 319-325. 

Fig. 8. Some possible arrangements of negatively charged proteins, cations, and the deprotonated PGE electrode surface. Upper. Cations bound in potential cavities at interface of protein and electrode. Middle Layer stabilized by cations binding at the protein-electrode interface and between adjacent protein molecules. Lower. Promotion of protein-electrode interaction by complex formation with a positively charged protein molecule...

A number of questions remain concerning the dynamics of the protein-electrode interaction. Do experimental data give any idea about the rates, relative or otherwise, of the electron-transfer step The clearest result so far has been the determination of ke, for horse heart cytochrome c at 4,4 -bipyridyl-modified Au with the rotating ring-disk technique as mentioned above [65], There have been a number of determinations of compound heterogeneous rate constants for protein electrochemistry, mostly using Nicholson s method [124] for their estimation from CV peak separations. All calculations have assumed that the mass transport can be treated in terms of linear diffusion to a uniform planar electrode surface. Bond and co-workers have pointed out [125,126] that in many instances this is unlikely to be... 

In addition to its quantitative aspects, adsorptive stripping voltammetry provides important contributions to our knowledge of biological compounds. In particular, considerable recent activity in our laboratory has focussed on the achievement of direct electron traiisfer for various biomacromolecules. The strategy here is to form the protein/-electrode complex , essential for a facile redox process, using an unmodified electrode. Electron-transfer rates are known to decay rapidly (exponentially) upon increasing the distance between the electrode and the redox center of the biomacromolecule. Binding of such molecules to the surface may thus be effective for electron-transfer enhancement. Other laboratories have concentrated on the use of electrode modifiers (e.g.,... 

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