Cytochrome electrochemical reduction

When the second-site revertants were segregated from the original mutations, the bci complexes carrying a single mutation in the linker region of the Rieske protein had steady-state activities of 70-100% of wild-type levels and cytochrome b reduction rates that were approximately half that of the wild type. In all these mutants, the redox potential of the Rieske cluster was increased by about 70 mV compared to the wild type (51). Since the mutations are in residues that are in the flexible linker, at least 27 A away from the cluster, it is extremely unlikely that any of the mutations would have a direct effect on the redox potential of the cluster that would be observed in the water-soluble fragments. However, the mutations in the flexible linker will affect the mobility of the Rieske protein. Therefore, the effect of the mutations described is due to the interaction between the positional state of the Rieske protein and its electrochemical properties (i.e., the redox potential of the cluster). 

To evaluate the functional role(s) of this residue, six mutations, Lys, His, Glu, Asn, Leu, and Ala, were introduced at this site, and the electrochemical and NMR properties of the resulting proteins examined [134]. Contrary to expectation, removal of Arg-38 did not result in a change in the dependence of the cytochrome c reduction potential on pH. Instead, as the electron-withdrawing ability of the residue substituted at position-38 decreased, the reduction potential also decreased, with the greatest decrease (50 mV) observed for the Ala mutant. The variation of reduction potential with pH, however, remained essentially the same as that previously observed for the wild-type protein. 

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. 

Matsuba D, Takazaki H, Sato Y, Takahashi R, Tokuyama T, Wakabayashi K (2003) Susceptibility of ammonia-oxidizing bacteria to nitrification inhibitors. Z Naturforsch 58c 282-287 Matsubara H, Smith EL (1963) Human heart cytochrome c. J Biol Chem 238 2732-2753 Matsumoto N, Nakasono S, Ohmura N, Saiki H (1999) Extension of logarithmic growth of Thiobacillus ferrooxidans by potential controlled electrochemical reduction of Fe(III). Biotechnol Bioeng 64 716-721... 

The possibility of electrochemical reduction and oxidation of cytochrome c on a gold electrode was demonstrated by means of spectroelectro-chemical measurements. The measurements were made in a cell with an optically transparent (grid) electrode, thus permitting the spectra to be recorded directly during electrochemical measurements. Figure 8 shows the spectra of the electrochemically reduced (curve 1) and oxidized (curve 2) cytochrome c. The spectra of ferro- and ferricytochrome c obtained electrochemically are identical with those of the chemically reduced and oxidized forms of cytochrome c. Investigations have also shown that after electrochemical reduction of the protein its enzymatic activity is preserved. ... 

Cytochrome C3 and Cj undergo direct electrochemical reduction at extremely fast rates compared to other cytochromes. Cytochromes C3 has four... 

Shumyantseva V, Buiko T, Archakov A (2005) Electrochemical reduction of cytochrome P450 as an approach to the construction of biosensors and bioreactors. J Inorg Biochem 99 1051-1063... 

Whereas in the zeolite system the [Fe +0] species is produced from N2O, in the biochemical system the biochemical oxidation step of the enzyme with O2 is coupled to an electrochemical reduction the overall reaction for cytochrome P-450 that converts the alkane to an alcohol is... 

The process of the reduction of oxygen to water in the mitochondria has been widely studied in the course of time. It is generally accepted that oxygen is reduced by cytochrome oxidase, the terminal enzyme in the electron transport chain, in a single 4-electron 4-proton step. However, the discussion about the true mechanism of the process is still not closed. The electrochemical reduction of oxygen has also been studied extensively by direct methods as well as indirectly in the presence of mediators - ... 

Figure 26 shows the redox potential of 40 monolayers of cytochrome P450scc on ITO glass plate in 0.1 KCl containing 10 mM phosphate buffer. It can be seen that when the cholesterol dissolved in X-triton 100 was added 50 pi at a time, the redox peaks were well distinguishable, and the cathodic peak at -90 mV was developed in addition to the anodic peak at 16 mV. When the potential was scanned from 400 to 400 mV, there could have been reaction of cholesterol. It is possible that the electrochemical process donated electrons to the cytochrome P450scc that reacted with the cholesterol. The kinetics of adsorption and the reduction process could have been the ion-diffusion-controlled process. 

Porphyrin complexes are particularly suitable cores to construct dendrimers and to investigate how the behavior of an electroactive species is modified when surrounded by dendritic branches. In particular, dendritic porphyrins can be regarded as models for electron-transfer proteins like cytochrome c [42, 43]. Electrochemical investigation on Zn-porphyrins bearing polyether-amide branches has shown that the first reduction and oxidation processes are affected by the electron-rich microenvironment created by the dendritic branches [42]. Furthermore, for the third generation compound all the observed processes become irreversible. 

G.C. Zhao, Z.Z. Yin, L. Zhang, and X.W. Wei, Direct electrochemistry of cytochrome c on a multi-walled carbon nanotube modified electrode and its electrocatalytic activity for the reduction of H2O2. Electrochem. Commun. 7, 256-260 (2005). 

These arguments were apparently in contradiction with electrochemical results reported by Cruanes et al. (158), according to which the reduction of cytochrome c is accompanied by a volume collapse of 24 cm3 mol-1. This value is so large that it almost represents all of the reaction volume found for the investigated reactions discussed above. A reinvestigation of the electrochemistry of cytochrome c as a function of pressure, using cyclic and differential pulse voltammetric techniques (155), revealed a reaction volume of -14.0 0.5 cm3 mol-1 for the reaction... 

The first electrochemical studies of Mb were reported for the horse heart protein in 1942 (94) and subsequently for sperm whale Mb (e.g., 95) through use of potentiometric titrations employing a mediator to achieve efficient equilibriation of the protein with the electrode (96). More recently, spectroelectrochemical measurements have also been employed (97, 98). The alternative methods of direct electrochemistry (99-102) that are used widely for other heme proteins (e.g., cytochrome c, cytochrome bs) have not been as readily applied to the study of myoglobin because coupling the oxidation-reduction eqiulibrium of this protein to a modified working electrode surface has been more difficult to achieve. As a result, most published electrochemical studies of wild-type and variant myoglobins have involved measurements at eqiulibrium rather than dynamic techniques. 

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