Bioelectrocatalysis

Enzymes are extremely important biomolecules because of their catalytic power and extraordinary specificity, superior to any synthetic catalyst. 

The activity of redox enzymes as biological catalysts depends, in some cases, on their protein structure. In other situations the presence of non-proteic cofactors is necessary the cofactors can be metals in the case of metalloenzymes, or organic molecules in the case of coenzymes (Table 17.3). 

Bioelectrocatalysis can be defined as the group of phenomena associated with the acceleration of electrochemical reactions in the presence of biological catalysts—the enzymes. 

For various reasons, it was only in the 1970s that enzymes began to be used as bioelectrochemical catalysts. Some of the reasons were difficulty in preparation of pure enzymes, their instability, and the lack of multiple applications. These problems have been largely overcome, and better purification methods and enzyme immobilization methods on electrode surfaces have been developed. 

The principal applications of biocatalysts in electrochemical systems can be summarized as  

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All these considerations have served as a basis for attempts at nsing various enzymes in electrochemical reactions. This field of research became known as bioelectrocatalysis. 

Ikeda T, Kobayashi D, Matsushita F, Sagara T, Niki K. 1993. Bioelectrocatalysis at electrodes coated with alcohol dehydrogenase, a quinohemoprotein with heme c serving as a built-in mediator. J Electroanal Chem 361 221-228. 

Kamitaka Y, Tsujimura S, Setoyama N, Kajino T, Kano K. 2007. Fructose/dioxygen biofuel cell based on direct electron transfer-type bioelectrocatalysis. Phys Chem Chem Phys 9 1793-1801. 

C. Cai and J. Chen, Direct electron transfer and bioelectrocatalysis of hemoglobin at a carbon nanotube electrode. Anal. Biochem. 325, 285-292 (2004). 

X.H. Chen, C.M. Ruan, J.L. Kong, and J.Q. Deng, Characterization of the direct electron transfer and bioelectrocatalysis of horseradish peroxidase in DNA film at pyrolytic graphite electrode. Anal. Chim. 

Y. Zhang, P.L. He, and N.F. Hu, Horseradish peroxidase immobilized in Ti02 nanoparticle films on pyrolytic graphite electrodes direct electrochemistry and bioelectrocatalysis. Electrochim. Acta 49, 1981-1988 (2004). 

J. Razumiene, M. Niculescu, A. Ramanavicius, V. Laurinavicius, and E. Csoregi, Direct bioelectrocatalysis at carbon electrodes modified with quinohemoprotein alcohol dehydrogenase from Gluconobacter sp. 33. Electroanalysis 14, 43—49 (2002). 

S. V. Morozov, E. E. Karyakina, N. A. Zorin, S. D. Varfolomeyev, S. Cosnier, A. A. Karyakin (2002) Direct and electrically wired bioelectrocatalysis by hydrogenase from Thiocapsa roseopersicina. Bioelectrochemistry, 55 169-171... 

Bioelectrocatalysis involves the coupling of redox enzymes with electrochemical reactions [44]. Thus, oxidizing enzymes can be incorporated into redox systems applied in bioreactors, biosensors and biofuel cells. While biosensors and enzyme electrodes are not synthetic systems, they are, essentially, biocatalytic in nature (Scheme 3.5) and are therefore worthy of mention here. Oxidases are frequently used as the biological agent in biosensors, in combinations designed to detect specific target molecules. Enzyme electrodes are possibly one of the more common applications of oxidase biocatalysts. Enzymes such as glucose oxidase or cholesterol oxidase can be combined with a peroxidase such as horseradish peroxidase. 

A.L. Ghindilis, T.G. Morzunova, A.V. Barmin and I.N. Kurochkin, Potentiometric biosensors for cholinesterase inhibitor analysis based on mediatorless bioelectrocatalysis, Biosens. Bioelectron, 11 (1996) 873-880. 

The mechanism and theory of bioelectrocatalysis is still under development. Electron transfer and variation of potential in the electrodeenzyme-electrolyte system has therefore to be investigated. Whether the enzyme is soluble and the electron transfer process occurs through a mediator, or whether there is direct enzyme immobilization on the electrode surface, the homogeneous process in the enzyme active centre has to be described by the laws of enzyme catalysis, and the heterogeneous processes on the electrode surface by the laws of electrochemical kinetics. Besides this there are other aspects outside electrochemistry or... 

Castillo J, Ferapontova E, Hushpulian D et al (2006) Direct electrochemistry and bioelectrocatalysis of H202 reduction of recombinant tobacco peroxidase on graphite. Effect of peroxidase single-point mutation on Ca2+-modulated catalytic activity. J Electroanal Chem 588 112-121... 

Belcarz A, Ginalska G, Kowalewska B, Kulesza P (2008) Spring cabbage peroxidases -Potential tool in biocatalysis and bioelectrocatalysis. Phytochemistry 69 627-636... 

Koper MTM, Heering HA. Comparison of Electrocatalysis and Bioelectrocatalysis, of Hydrogen and Oxygen Redox Reactions. In Wieckowski A, Norskov JK, editors. Fuel cell science. Hoboken, NJ Wiley-VCH 2010. Chapter 2. 

The first reports on a reversible DET between redox proteins and electrodes were published in 1977 showing that cytochrome c is reversibly oxidized and reduced at tin-doped indium oxide [30] and gold in the presence of 4,4 -bipyridyl [31]. Only shortly after these publications appeared, papers were published describing the DET between electrode and enzyme for laccase and peroxidase [32,33]. It was observed that the overpotential for oxygen reduction at a carbon electrode was reduced by several hundred millivolts compared to the uncatalyzed reduction when laccase was adsorbed. This reaction could be inhibited by azide. The term bioelectrocatalysis was introduced for such an acceleration of the electrode process by... 

The electron donor can be substituted by an electrode (Eq. (2.7)), thereby enabling mechanistic studies, estimations of ET rates and bioelectrocatalysis. The latter has currently gained particular interest for the development of biofuel cells [248,249] and virtually reagentless immunosensors [7,250]. 

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