Protein electrochemical reactions

Ionic liquids (ILs) are expected to be unique solvents for electrochemical reactions because of their extraordinary properties. ILs can dissolve a wide variety of molecules and materials. ILs are excellent solvents for the bioelectrochemistry field, but great care must be taken with the procedure of solubilization because most biomaterials such as proteins and enzymes are characterized by higher ordered stractures that have an origin in their numerous functions. Therefore consideration must be given to the structural changes of biomaterials when they are dissolved in ILs. 

The electrochemical reactions involving protein at the metal interface has been related to adsorption and charge transfer (12, 13, 41). When Far-adaic currents (if) occur, the total current (i) is given by (44),... 

In the present system with the copper-2% zinc electrodes, all three processes of protein adsorption, charge transfer, and Faradaic oxidations and reductions are possible. The peaks observed in the anodic and cathodic processes are related, respectively, to oxidations and reductions of the electrode. Copper oxides, chlorides, basic chlorides, phosphates, etc., as well as zinc products, are probable compounds for these electrochemical reactions. Increased Faradaic processes and charge transfer processes with protein solutions are factors for increasing the j-U profiles at U s less than +0.3 V. Since the sweep rate is a constant here, the capacitance of the double layer must increase for the protein solutions, if the increase in j is not all due to Faradaic processes One analog of the electrical double layer capacitance incorporates three capacitors in series (44). Hence... 

Munge B, Pendon Z, Frank HA et al. Electrochemical reactions of redox cofoctors in Rhodobacter sphaeroides reaction center proteins in lipid films. Bioelectrochem 2001 54 145-150. 

Studies of electrochemical reactions of redox proteins have attracted widespread interest and attention. Such studies can yield important information about not only intrinsic thermodynamic and kinetic properties of redox proteins, but also structural properties, such as binding characteristics of proteins at specific types of electrode surfaces and the orientational requirements for electron transfer between the protein and the electrode. The results are useful for the development of biosensors, biofuel cells, and biocatalysts. In addition, the information obtained from these studies can contribute to an understanding of the physiological implications of biological electron transfer reactions, because many electron transfer proteins are located at, or close to, charged membranes and are thus subject to large electric field effects that are similar to those near an electrode surface. 

Principles Redox Protein Systems. In most cases, redox proteins undergo extremely slow electron transfer reactions at electrodes. Therefore, the thermodynamic parameters cannot be determined directly from the equations described above. One method for resolving this problem is to add a mediator, M, to the solution. The mediator shuttles electrons between the electrode and the protein and thereby accelerates the electrochemical reaction of the protein. A reversible or quasi-reversible electron transfer reaction of the redox protein, P, is then achieved indirectly through the mediator as shown in Scheme I. The Nernst equation is... 

V. Electrochemical Reactions of Redox Proteins at Chemically Modified Electrodes... 

Other phenothiazine dyes, such as methylene green (MG), brilliant cresyl blue (BCB), janus green (JG), toluidine blue (TB), and azure A (AA), can also be immobilized on Pt electrode surfaces by adsorption and the cyclic potential scan method used to prepare MB CMEs." The MG, BCB, JG, TB, and AA CMEs were all found to facilitate effectively the electrochemical reactions of redox proteins and the modified... 

To increase the stability of the phenothiazine dye CMEs, investigations of the electrochemical reactions of redox proteins at polymer CMEs have been undertaken. One example of such a study is the heterogeneous redox reaction of Cyt c at an electrochemically polymerized polypyrrole-methylene blue (PPy-MB) film CME. Figure 17 shows the cyclic voltammetric response that occurs during the preparation of this CME by potential... 

Since the establishment of spectroelectrochemistry very little effort has been devoted to the direct electrochemistry of redox proteins. Although many thermodynamic and kinetic parameters can be determined by UV-VIS spectroelectrochemistry, the electrochemical reaction mechanisms for redox proteins are not well understood. New techniques md new theoretical treatments are needed to address this issue. Moreover, most attention has been placed on relatively simple electron transfer proteins to date no one has reported the direct electrochemistry of a more complex system (e.g., a redox enzyme system) which unequivocally undergoes electron transfer to (or from) its active site. Considerable experimental work is needed to develop more fully spectroelectrochemical methods for biological systems. 

Cotton et al. Already in their preliminary work, the authors explored the potentialities and goals of the SERRS technique for possible applications to bioanalytical problems. The first possibility is enhanced sensitivity for the RR scattering of scarce materials. A second possibility can be added specifically to redox-active chromophores in proteins. Indeed, this new spectroelectrochemical method permits the simultaneous study of an electrochemical reaction in a biological system in conjunction with a specific measurement of subtile variations in the vibrational spectrum of the chromophores. Another striking feature of the SERRS spectroscopy is that fluorescence of the adsorbate can be completely quenched by the metal surface which generates a high-quality Raman spectrum Another common application of SERRS spectroscopy is the study of the adsorption behaviour and conformation of biomolecules at the metal/electrolyte interface. 

The structure and physicochemical properties of the enzymes which have been used to date to promote electrochemical reactions are briefly outlined. Methods of their immobilization are described. The status of research on redox transformations of proteins and enzymes at the electrode-electrolyte interface is discussed. Current concepts on the ways of conjugation of enzymatic and electrochemical reactions are summarized. Examples of bioelectrocatalysis in some electrochemical reactions are described. Electrocatalysis by enzymes under conditions of direct mediatorless transport of electrons between the electrode and the enzyme active center is considered in detail. Lastly, an analysis of the status of work pertaining to the field of sensors with enzymatic electrodes and to biofuel cells is provided. 

In this section we shall briefly discuss the structure and functional specificities of proteins and enzymes for which data are available on their electrochemical behavior and on their acceleration of electrochemical reactions. 

Much progress in the study of electrochemical properties of protein macromolecules has been achieved recently using another method, namely, the study of redox transformations of proteins, the carriers of electrons and enzymes, and their active groups at the electrode-electrolyte interface. This approach is intimately related to the use of enzymes to promote electrochemical reactions and pursues the purpose of elucidation of the mechanism of electron transport and the structural features of enzymes. 

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