Direct glucose oxidase

Entrapment of biochemically reactive molecules into conductive polymer substrates is being used to develop electrochemical biosensors (212). This has proven especially useful for the incorporation of enzymes that retain their specific chemical reactivity. Electropolymerization of pyrrole in an aqueous solution containing glucose oxidase (GO) leads to a polypyrrole in which the GO enzyme is co-deposited with the polymer. These polymer-entrapped GO electrodes have been used as glucose sensors. A direct relationship is seen between the electrode response and the glucose concentration in the solution which was analyzed with a typical measurement taking between 20 to 40 s. 

False. D-gluconolactone is produced directly from glucose via glucose oxidase. 6-phosphogluconolactone is an intermediate in the hexose monophosphate pathway. 

Further improvements can be achieved by replacing the oxygen with a non-physiological (synthetic) electron acceptor, which is able to shuttle electrons from the flavin redox center of the enzyme to the surface of the working electrode. Glucose oxidase (and other oxidoreductase enzymes) do not directly transfer electrons to conventional electrodes because their redox center is surroimded by a thick protein layer. This insulating shell introduces a spatial separation of the electron donor-acceptor pair, and hence an intrinsic barrier to direct electron transfer, in accordance with the distance dependence of the electron transfer rate (11) ... 

Pishko MV, Katakis I, Lindquist SE, Ye L, Gregg BA, Heller A. 1990. Direct electron exchange between graphite electrodes and an adsorbed complex of glucose oxidase and an osmium-containing redox polymer. Angew Chem 102 109-111. 

Y. Degani and A. Heller, Direct electrical communication between chemically modified enzymes and metal electrodes. I. Electron transfer from glucose oxidase to metal electrodes via electron relays, bound covalently to the enzyme. J. Phys. Chem. 91, 1285-1289 (1987). 

C. Cai and J. Chen, Direct electron transfer of glucose oxidase promoted by carbon nanotubes. Anal. Biochem. 332, 75-83 (2004). 

Y.D. Zhao, W.D. Zhang, H. Chen, and Q.M. Luo, Direct electron transfer of glucose oxidase molecules adsorbed onto carbon nanotube powder microelectrode. Anal. Sci. 18, 939-941 (2002). 

J. Liu, A. Chou, W. Rahmat, M.N. Paddon-Row, and J.J. Gooding, Achieving direct electrical connection to glucose oxidase using aligned single walled carbon nanotube arrays. Electroanalysis 17, 38—46 (2005). 

A. Guiseppi-Elie, C.H. Lei, and R.H. Baughman, Direct electron transfer of glucose oxidase on carbon nanotubes. Nanotechnology 13, 559-564 (2002). 

R.M. Ianniello, T.J. Lindsay, and A.M. Yacynych, Differential pulse voltammetric study of direct electron transfer in glucose oxidase chemically modified graphite electrodes. Anal. Chem. 54, 1098-1101 (1982). 

L. Jiang, C.J. McNeil, and J.M. Cooper, Direct electron transfer reaction of glucose oxidase immobilized at a self-assembled monolayer. J. Chem. Soc. Chem. Commun. 1293-1295 (1995). 

L. Wang and Z.B. Yuan, Direct electrochemistry of glucose oxidase at a gold electrode modified with single-wall carbon nanotubes. Sensors 3, 544-554 (2003). 

S.Q. Liu and H.X. Ju, Reagentless glucose biosensor based on direct electron transfer of glucose oxidase immobilized on colloidal gold modified carbon paste electrode. Biosens. Bioelectron. 19, 177-183 (2003). 

Y. Liu, M.K. Wang, F. Zhao, Z.A. Xu, and S.J. Dong, The direct electron transfer of glucose oxidase and glucose biosensor based on carbon nanotubes/chitosan matrix, Biosens. Bioelectron. 21, 984-988... 

Y.H. Wu and S.S. Hu, Direct electrochemistry of glucose oxidase in a colloid Au-dihexadecylphos-phate composite film and its application to develop a glucose biosensor. Bioelectrochemistry. Available online 6 May (2006). 

In contrast to the mediator-modified electrodes, Degani et al. modified glucose oxidase itself by means of covalently bound ferrocene [4]. After modifying enzymes with ferrocene carboxylic acid, they observed direct electron transfer from the active site of the enzyme to a gold or platinum... 

Schuman et al. have synthesized ferrocene-modified glucose oxidase with the ferrocene derivatives bound via long and flexible chains directly to the outer surface of the enzyme [17]. A peripherally attached redox mediator may accept electrons through either an intramolecular or through an intermo-lecular process. 

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