Proteins electrochemical properties

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). 

In the intermediate state, the Rieske protein interacts neither with cytochrome b nor with cytochrome Ci the existence of this state is consistent with the fact that the electrochemical properties of the Rieske protein are apparently unperturbed within the bci complex. 

Because of the exposed histidine ligands of the [2Fe-2S] cluster, the Rieske is capable of binding quinones in a redox-dependent manner. The variation of the hydrogen bond strength and of the electrostatic properties will control the movement of the catalytic domain of the Rieske protein. Therefore, the function depends on the unique structural and electrochemical properties of the Rieske cluster. 

A more complete list of early applications of QM/MM methods to enzymatic reactions can be found elsewhere [18, 35, 83, 84], Gao [85] has reviewed QM/MM studies of a variety of solution phenomena. QM/MM methods have also been used to study the spectra of small molecules in different solvents [86] and electrochemical properties of photosynthetic reaction centers within a protein environment [87-89], An approach has also been developed for calculation of NMR shielding tensors by use of a QM/ MM method [90]. 

The current chapter focuses on the electrochemistry of the ionic forms of copper in solution, starting with the potentials of various copper species. This includes the effect of coordination geometry, donor atoms, and solvent upon the electrochemical potentials of copper redox couples, specifically Cu(II/I). This is followed by a discussion of the various types of coupled chemical reactions that may contribute to the observed Cu(II/I) electrochemical behavior and the characteristics that may be used to distinguish the presence of each of these mechanisms. The chapter concludes with brief discussions of the electrochemical properties of copper proteins, unidentate and binuclear complexes. 

It has been known that adsorption kinetics and/or thermodynamics of proteins depend on the electric or electrochemical properties of solid supports on which the proteins are adsorbed. This has led us to elucidate the effects of electrode potential on the adsorption behavior of avidin on the electrode surface. For this purpose, the electrode potential of a Pt electrode was varied systematically in the range of -0.5-+2.0 V in an avidin solution (pH 7.4). Although the data was somewhat scattered, a general trend was observed that the adsorption of avidin is suppressed by the application of a positive potential (+1.0-+2.0 V). This may be originating from the fact that avidin is a basic protein and has net positive charges in the solution of neutral pH. In the potential range tested, no significant acceleration in the adsorption was induced. 

However, the electrochemical properties of such a complex are certainly very interesting since it represents a synthetic model for the activity of redox proteins and may mimic their capability to store reducing power in an oxidizing environment. 

The hydrophobias are a case where protein nanofibers can play a dual role in creating a biosensor. They can aid in the immobilization of bioactive components within a biosensor and also add further functionality to the transducing element of a biosensor device. Hydrophobins are self-assembling [3-sheet structures observed on the hyphae of filamentous fungi. They are surface active and aid the adhesion of hyphae to hydrophobic surfaces (Corvis et al., 2005). These properties can be used to create hydrophobia layers on glass electrodes. These layers can then facilitate the adsorption of two model enzymes glucose oxidase (GOX) and hydrogen peroxidase (HRP) to the electrode surface. The hydrophobin layer also enhances the electrochemical properties of the electrodes. 

Mitochondrial cytochrome c is the most widely investigated heme protein with respect to its electrochemical properties. It is active in electron transfer pathways such as the respiratory chain in the mitochondria where it transfers electrons between membrane bmmd C3d ochrome reductase complex III and cytochrome c oxidase. The active site is an iron porphyrin (heme) covalently linked to the protein at Cysl4 and Cysl7 through thioether bonds (heme c). The iron itself lies in the plane of the porphyrin ring, the two axial positions... 

Mitochondrial cytochrome c is perhaps the most widely studied of all metalloproteins with respect to its electrochemical properties. It is located in the inner-membrane space of mitochondria and transfers electrons between membrane-bound complex III and complex IV. The active site is an iron porphyrin with a redox potential (7) of -1-260 mV vs. NHE. The crystal structures of cytochrome c from tuna have been determined (8, 9) in both oxidation states at atomic resolution. It is found that the heme group is covalently linked to the protein via two thioether bridges, and part of its edge is exposed at the protein surface. Cytochrome c is a very basic protein, with an overall charge of -1-7/-l-8 at neutral pH. Furthermore, many of the excess basic lysine residues are clustered around the mouth of the heme crevice, giving rise to a pronounced charge asymmetry. 

In this chapter, we review the recent progress in the development of different metal oxide nanoparticles with various shapes and size for fabrication of biosensors. The development of metal oxide nanomaterials surface film for direct electron exchange between electrodes and redox enzymes and proteins will be summarizing. The electrochemical properties, stability and biocatalytic activity of the proposed biosensors will be discussed. The biocompatibility of the metal oxide nanomaterials for enzymes and biomolecules will be evaluated. We will briefly describe some techniques for the investigation of proteins and enzymes when adsorbed to the electrode surfaces. Cyclic voltammetry, impedance spectroscopy, UV-visible spectroscopy and surface imaging techniques were used for surface characterization and bioactivity measuring. 

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