Redox proteins electrical wiring

Electrical Wiring of Redox Proteins by Supramolecular Nanoparticle or Carbon Nanotube Hybrid Systems... 

Methods to electrically wire redox proteins with electrodes by the reconstitution of apo-proteins on relay-cofactor units were discussed. Similarly, the application of conductive nanoelements, such as metallic nanoparticles or carbon nanotubes, provided an effective means to communicate the redox centers of proteins with electrodes, and to electrically activate their biocatalytic functions. These fundamental paradigms for the electrical contact of redox enzymes with electrodes were used to develop amperometric sensors and biofuel cells as bioelectronic devices. 

Since the iron center of the protein was not shielding, the electron transfer occurred and cyclic voltammograms showed a voltanunogram with a redox couple with E1/2 at -390 mV. The eoverage obtained from the reduction peak area was 35 pmolcm, well correlated with the the value of 32 pmolcm" estimated from the AFM images. In summary, the SWCNT normal aligned can act as molecular wires to allow the electrical commrmication between the electrode and redox proteins covalently attached to the ends of SWCNTs. 

The chemical modification of redox enzymes with electron relay groups permits the mediated electron transfer and the electrical wiring of the proteins [83-85] (Figure 5A). The covalent attachment of electron-relay units at the protein periphery, as well as inner sites, yields short inter-relay electron-transfer distances. Electron hopping or tunneling between the periphery and the active site allows electrical communication between the redox enzyme and its environment. The simplest systems of this kind involve electron relay-functionalized enzymes diffusionally communicating with electrodes [83], but more complex assemblies including immobilized enzymes have also been reported. 

Figure 39. Electrical communication between an enzyme redox center and a photoexcited species attaining light-induced biocatalyzed transformations (A) direct electrical wiring of the protein by its chemical modification with tethered electron-relay units (B) electrical communication by the immobilization of the protein into a redox-functionalized polymer matrix.

Heller A 1990 Electrical wiring of redox enzymes Accounts Chem. Res. 23 128-34 Lisman J E and Goldring M A 1988 Feasibility of long-term storage of graded information by the Ca" /calmoduIin-dependent protein kinase molecules of the postsynaptic density Proc. Natl Acad. Sci. USA 85 5320-4 Anelli P L, Spencer N and Stoddart J F 1991 A molecular shuttle J. Am. Chem. Soc. 113 5131-3... 

The rate constant for ET from the redox polymer functionalities to the protein active site is k, = (9 + 3) x 10 s. Similarly, the enzyme glutathione reductase was electrically wired by interacting the protein with a redox polymer composed of polylysine modified by JV-methyl-JV -carboxy-alkyl-4,4 -bipyridinium. The photosensitized reduction of oxidized gluta-... 

The electrostatic control of the electrical contact between redox-proteins and electrodes by means of command interfaces was further demonstrated by the photochemical switching of the bioelectrocatalytic properties of glucose oxidase (Figure 7.22). Ferrocene units were tethered to the protein backbone of glucose oxidase to yield an electrically wired enzyme that is activated for the bioelectrocatalyzed oxidation of glucose. The enzyme is negatively charged at neutral pH values (pIc,o 4.2 ) and, hence, could be... 

Direct unmediated electrical communication between enzyme redox centers and the electrode by molecular wiring has been attracting attention recently/ In this technique the natural ability of polyanionic oxidoreductases to form electrostatic complexes with redox proteins for effective electron transfer can be applied in biosensor technology. However, in place of the redox protein, a polycationic redox macromolecule is used. The result is a three-dimensional network of an electrostatic complex of the enzyme and the redox polymer. In this system membranes are not needed, nor is unique orientation of the enzymes necessary. This is... 

Therefore, it can be concluded that the redox proteins (c-type cytochrome etc.) and electrodes comprise the main part of DET. The increased contact of the redox proteins (c-type cytochrome etc.) and electrodes would be helpful to DET, thereby influencing the MFC efficiency. Evidence has revealed that some conductive polymers could act as electrical wiring between cells and anodes (Table 5.2). 

Direct electrical wiring of the enzyme to the electrode is established when the active redox center can directly be regenerated by the electrode. In this case, by considering different structures of enzymes and its location of the active site inside the protein, different strategies for their wiring are to evaluate. Indeed, direct electron tranfer becomes a challenge when the active site is deeply embedded inside the protein and cannot exchange electrons without the need of redox mediators. 

Supramolecular assemblies/architectures represent an alternative approach to electrically connecting redox proteins with electrodes. For example, bis-bipyridinium cyclophane has been threaded onto a molecular wire assembled on an electrode by the formation of an intermediary pdonor-acceptor bond with the bis-imine-benzene site of the molecular wire [4]. The wire was then stoppered by an adamantane stopper unit to form a supramolecular assembly. The charged cyclophane could then be moved along the wire by electrochemi-cally changing its oxidation state. Reduction of the cyclophane to the bis-radical cation removed the electron acceptor properties of the threaded ring, and the reduced acceptor was electrostatically attracted by the electrode. This resulted in translocation of the reduced cyclophane to the electrode with a rate constant corresponding to k = 320 s. Oxidation of the reduced cyclophane reversed the direction of movement. 

As mentioned earlier, observations of direct voltammetry of biomolecules, especially proteins, can be limited at flat, bulk-material electrodes due to problems with electrode fouling, biomolecule denaturation, and accessibility of redox centers." " Various approaches (e.g., protein-film electrodes and electrical wiring of proteins to electrodes) have been employed to address these issues. However, strategies that employ nanomaterials to conduct bioelectrochemical studies have become increasingly popular for bioelectrochemical applications as nanomaterials have become readily available and have been shown to possess properties (e.g., high specific areas and excellent electron-transfer characteristics) that are favorable to bioelectrochemistry. 

Willner and coworkers have extended this approach to electron relay systems where core-based materials facilitate the electron transfer from redox enzymes in the bulk solution to the electrode.56 Enzymes usually lack direct electrical communication with electrodes due to the fact that the active centers of enzymes are surrounded by a thick insulating protein shell that blocks electron transfer. Metallic NPs act as electron mediators or wires that enhance electrical communication between enzyme and electrode due to their inherent conductive properties.47 Bridging redox enzymes with electrodes by electron relay systems provides enzyme electrode hybrid systems that have bioelectronic applications, such as biosensors and biofuel cell elements.57... 

---