Redox proteins, electrochemistry

Parker VD, Seefeld LC. A Mediated thin-layer voltammetry method for the study of redox protein electrochemistry. Anal Biochem 1997 247 152-157. 

In this chapter we first describe components and the organization of some important biological redox systems. We then discuss advantages of electroactive polymers for this type of application and review the work so far in different areas of redox protein electrochemistry, redox enzyme electrochemistry, and redox... 

In contrast to the area of redox protein electrochemistry, redox enzyme electrochemistry has received much greater attention, driven in many cases by the desire to construct practical, self-contained enzyme electrodes for commercial applications. Redox enzyme electrochemistry is also easier to study in many ways because the substrate or product is often detected electrochemically rather than the enzyme itself. Various types of electroactive polymers have been used with redox enzymes, including redox polymers, redox-active hydrogels, and electropolymer-ized films of conducting and nonconducting, polymers. We discuss each type of polymer in turn, starting with electropolymerized films. 

Coleman, J.O.D., Hill, H.A.O., Walton, N.J. and Whatley, F.R. (1984) "Electrochemically-driven electron Transport in Biological Systems The Exploitation of Direct Redox-protein Electrochemistry". In "Charge and Field Effects in Biosystems". Eds. M. J. Allen and P. N. R. Usherwood, Abacus Press, London, 1984, pp. 61-68... 

Since, in redox protein electrochemistry, electrode and the protein redox centre are usually considered as a donor-acceptor pair, the distance or spatial separation of the protein redox centre from the electrode by means of the protein shell prohibits the direct electrical communication between the redox site and the electrode. 

Nowadays, studies of direct electrochemistry of redox proteins at the electrodesolution interface have held more and more scientists interest. Those studies are a convenient and informative means for understanding the kinetics and thermodynamics of biological redox processes. And they may provide a model for the study of the mechanism of electron transfer between enzymes in biological systems, and establish a foundation for fabricating new kinds of biosensors or enzymatic bioreactors. 

The first reports on direct electrochemistry of a redox active protein were published in 1977 by Hill [49] and Kuwana [50], They independently reported that cytochrome c (cyt c) exhibited virtually reversible electrochemistry on gold and tin doped indium oxide (ITO) electrodes as revealed by cyclic voltammetry, respectively. Unlike using specific promoters to realize direct electrochemistry of protein in the earlier studies, recently a novel approach that only employed specific modifications of the electrode surface without promoters was developed. From then on, achieving reversible, direct electron transfer between redox proteins and electrodes without using any mediators and promoters had made great accomplishments. 

The determination of H202 is very important in many different fields, such as in clinical, food, pharmaceutical, and environmental analyses [202], Many techniques such as spectrophotometry, chemiluminesence, fluorimetry, acoustic emission, and electrochemistry methods have been employed to determine H202. Electrochemical methods are often used because of their advantages. Among these electrochemical methods, the construction of the mediator-free enzyme-based biosensors based on the direct electrochemistry of redox proteins has been reported over the past decade [203— 204], The enzyme-based biosensors, which use cyt c as biocatalyzer to catalyze H202, were widely studied. 

C. The Microscopic Model in Protein Electrochemistry Electrochemistry of Protein-Protein Complexes Electrochemistry of Redox Enzymes... 

One of the first reports on the quasireversible electrochemistry of redox proteins appeared in 1977 when Eddowes and Hill demonstrated (10) cyclic voltammetry of horse heart cytochrome c at a gold electrode in the presence of 4,4 -bipyridyl (Bipy) in solution. In the voltammo-grams (Fig. 1), the peak-to-peak separations were close to 60 mV and the faradaic currents varied linearly with (scan rate), indicating a quasireversible one-electron transfer process controlled by linear diffusion of redox species to the electrode surface. The midpoint potential... 

Direct, unmediated electrochemistry of redox enzymes has interested many researchers in several aspects. Understanding of the thermodynamics, kinetics, stoichiometry, and interfacial properties of redox enzymes is obviously important. The most attractive aspect, however, is the use of enzyme electrodes as novel electrochemical biosensors and their applications to bioreactors and biofuel cells. Although the observation of direct electrochemistry of small redox proteins has become almost commonplace as the consequence of extensive research over the past decade, the corresponding study with larger redox enzymes has proved more elusive. The difficulty lies mainly in that the redox centers are located sufficiently far from the outermost... 

Direct electrochemistry has also been used (72-78) to couple the electrode reactions to enzymes for which the redox proteins act as cofactors. In the studies, the chemically reduced or oxidized enzyme was turned over through the use of a protein and its electrode reaction as the source or sink of electrons. In the first report (72, 73) of such application, the electrochemical reduction of horse heart cjd,ochrome c was coupled to the reduction of dioxygen in the presence of Pseudomonas aeruginosa nitrite reductase/cytochrome oxidase via the redox proteins, azurin and cytochrome C551. The system corresponded to an oxygen electrode in which the four-electron reduction of dioxygen was achieved relatively fast at pH 7. 

The direct electrochemistry of redox proteins has developed significantly in the past few years. Conditions now exist that permit the electrochemistry of all the proteins to be expressed at a range of electrodes, and important information about thermodynamic and kinetic properties of these proteins can be obtained. More recently, direct electron transfer between redox enzymes and electrodes has been achieved due to the more careful control of electrode surfaces. The need for biocompatible surfaces in bioelectrochemistry has stimulated the development of electrode surface engineering techniques, and protein electrochemistry has been reported at conducting polymer electrodes 82) and in membranes 83, 84). Furthermore, combination of direct protein electrochemistry with spectroscopic methods may offer 85) a novel way of investigating structure-function relationships in electron transport proteins. 

It is very important to define criteria to unequivocally proof a direct ET pathway between an immobilized redox protein and an electrode surface. The first important prerequisite is the occurrence of the direct electrochemistry of the redox cofactor inside the protein in the absence of the substrate. Hence, a reversible redox wave in a cyclic voltammogram of the protein-integrated cofactor has to be visible with a formal potential which clearly shows that the protein structure is not... 

Armstrong, F.A., George, S.J., Thomson, A.J., and Yates, M.G. (1988) Direct electrochemistry in the characterization of redox proteins-novel properties of Azobacter 7Fe ferredoxin. FEES Letters, 234 (1), 107-110. 

B. N., and Walton, N.J. (1984) Direct electrochemistry of redox proteins at pyrolytic graphite electrodes. Journal of... 

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