Redox Potentials Of Proteins Research Articles

Characterising the formation of a bioelectrochemical interface at a self-assembled monolayer using X-ray photoelectron spectroscopy

In this paper, we characterise the process of immobilisation of cytochrome c at a gold surface modified with the short chain alkyl-thiol self-assembled monolayer, mercaptopropionic acid. Using high resolution X-ray photoelectron spectroscopy, we reveal detail of the step-by-step construction of the biomolecular structure at a self-assembled monolayer, measured during two different immobilisation protocols involving either a carbodiimide activated intermediate or aminolysis of a succinimide ester by the protein. Finally, we relate the subtle variations in the charged species produced during the immobilisation procedures to differences that we measure in the protein's redox potential.

A Mediated Thin-Layer Voltammetry Method for the Study of Redox Protein Electrochemistry

A novel mediated thin-layer voltammetry technique that allows the rapid determination of midpoint potentials and electron transfer rate constants for small quantities of redox active proteins is described. Thin-layer voltammograms simulated for an electrolyte containing a redox active protein and an electron transfer mediator show that the rapid homogeneous electron exchange reaction between the protein and the mediator serves to mediate the charge transfer of the protein at the electrode, which does not take place in the absence of the mediator, and results in the observation of an apparently reversible redox couple. Both theoretical and experimental data are presented which suggest that the thin-layer voltammetry method will be generally applicable for the determination of protein redox potentials with the proper selection of mediators. Rate constants for the electron transfer between metalloproteins and mediators can be evaluated by comparing experimental voltammograms with theoretical data from simulations. The technique is demonstrated for the metalloproteins cytochrome c, ferredoxin, and the iron protein of nitrogenase.

Microscopic and semimacroscopic redox calculations: what can and cannot be learned from continuum models

The major role of electrostatic effects in the control of redox potentials in proteins is now widely appreciated. However, the evaluation and conceptualization of the actual electrostatic contributions is far from trivial, and some models still overlook the nature of electrostatic effects in proteins. This commentary considers different contributions to redox potentials of proteins and discusses the ability of different models to capture these contributions. It is pointed out that macroscopic models which consider the protein as a medium of uniform low dielectric constant cannot reproduce the proper physics of redox proteins. In particular, it is pointed out that the crucial effects of the protein permanent dipoles must be taken into account explicitly and that these permanent dipoles involve effective dielectric constants that are different from those for ionized residues. It is also argued that the reorganization of the protein upon change of oxidation states or ionization of protein residues should be taken into account in redox calculations. The role of water penetration and the inadequacy of describing electrostatic effects by solvent accessibility is briefly mentioned. The nature and the meaning of the "dielectric constant" that should be used in redox calculations are also discussed. It is pointed out that the "dielectric constant" ep used in current discretized continuum (DC) models is simply a representation of the contributions which are treated implicitly and not the proper dielectric constant of the protein. It is then explained that the need to use a large "dielectric constant" in DC models reflects, among other factors, the implicit representation of the reorganization of permanent dipoles, and that even an explicit treatment of the fluctuations of ionized surface residues will lead to incorrect results when one uses ep=e¯ in continuum treatments. Finally, it is suggested that although the discussion and classification of different contributions to redox potentials is very useful, only the evaluation of the totality of the protein contributions (rather than an arbitrary subset) can lead to a quantitative understanding of redox proteins.

Medium effects on the redox properties of tris(2,2′-bipyridyl)ruthenium complexes

The electrochemisty of the 2,2′-bipyridyl ruthenium complexes [Ru(Bipy) 3] n± has been examined in a series of solvents with varying dielectric constant. The potential separation between the +1/0 and 0/−1 redox steps increases with decreasing solvent polarity and decreasing ionic strength of the supporting electrolyte. Electrochemically generated [Ru(Bipy) 3] n (where n = 0 or −1) is kinetically labile in these low oxidation states and capable of reacting with the very high dielectric solvent N-methylacetamide via an E rC i mechanism; k f for the following chemical reaction is 0.31±0.15 s −1. Relationship is drawn between the dependence of the [Ru(Bipy) 3] potentials on solvent dielectric and the effect of local dielectric on protein redox potentials, and comment is made also on the solvent dependence of the potential of the ferricenium/ferrocene couple.

Control of heme protein redox potential and reduction rate: linear free energy relation between potential and ferric spin state equilibrium

Control of heme protein redox potential and reduction rate: linear free energy relation between potential and ferric spin state equilibrium

Potentiodynamic and spectroelectrochemical studies of the cytochrome c and some other iron-containing complexes

The results of potentiodynamic and spectroelectrochemical studies of cytochrome c, peroxidase, ferredoxin and hemin are described. It was shown that cytochrome c can be reduced and oxidized electrochemically retaining its molecular structure. The electrochemical reactions of cytochrome c occur at a considerable overvoltage. The comparison of the redox potentials of proteins in native state and during electrochemical transformations showed that the electrochemical reactions occur in the potential range differing from the reversible potential by ∼0,3 V. On the contrary, the redox reactions of hemin occur in the vicinity of the reversible potential of thie iron complex. Non-heme iron in ferredoxin is also reduced without overvoltage. These differences in the behavior of cytochrome c and non-protein iron-containing complexes seem to be due to the conformational peculiarities of proteins in dissolved and adsorbed states.