Enzyme electrochemistry reductase

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. 

Microperoxidase-11, MP-11, is a heme-undecapeptide that is prepared by the digestion of cytochrome c and it includes the active surrounding of cytochrome MP-11 was immobilized on electrode surface s and its electrochemistry was characterized. The MP-11-modified electrodes were reported to act as effective electron mediator interfaces for the reduction of cytochrome c, hemoglobin, myoglobin and nitrate reductase (cytochrome c-dependent). The MP-11-mediated activation of nitrate reductase, NR, was employed to assemble an integrated MP-11/NR electrode for the bioelectrocatalyzed reduction of nitrate (NO3 ) to nitrite (NO2). An affinity complex between a MP-11-functionalized electrode and NR (/Q = 3.7x10 M ) was crosslinked with glutaric dialdehyde to yield the electrically contacted electrode for the bioelectrocatalyzed reduction of nitrate to nitrite. In this system the reduced MP-11 mediates ET to NR and activates the enzyme towards the reduction of NO3. 

Figure 5.1 (a) Mediated Mo enzyme (reductase) electrochemistry and (b) direct Mo... 

The Butt group has reported direct electrochemistry of NapAB from Paracoccus pantotrophusf The same potential dependent catalytic currents seen for R. sphaeroid.es NapAB are also found for this system (Figure 5.27). In addition, significant selenate reductase activity was demonstrated for this enzyme. 

To predict systems most likely to yield meaningful and useful direct electrochemistry, redox enzymes may be divided into two categories. The first comprises those for which one of the redox processes in the catalytic cycle is a discrete outer-sphere (and probably long-range) electron-transfer reaction. Examples include the blue Cu oxidases, ferredoxin-linked reductases, and cytochrome c oxidase and other enzymes of electron-transport chains. In such systems there is exchange of electrons with an extrinsic agent, i.e. one that does not form... 

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