Enzymes glucose oxidase

Figure 11.39 summarizes the reactions taking place in this amperometric sensor. FAD is the oxidized form of flavin adenine nucleotide (the active site of the enzyme glucose oxidase), and FAD1T2 is the active site s reduced form. Note that O2 serves as a mediator, carrying electrons to the electrode. Other mediators, such as Fe(CN)6 , can be used in place of O2. 

This experiment describes the use of a commercially available amperometric biosensor for glucose that utilizes the enzyme glucose oxidase. The concentration of glucose in artificial... 

Commercially available kits for monitoring blood-glucose use an amperometric biosensor incorporating the enzyme glucose oxidase. This experiment describes how such monitors can be adapted to the quantitative analysis of glucose in beverages. 

Chemical kinetic methods have been applied to the quantitative analysis of a number of enzymes and substrates.One example, is the determination of glucose based on its oxidation by the enzyme glucose oxidase. ... 

In presence of the enzyme glucose oxidase, an aqueous solution of glucose undergoes oxidation to gluconic acid with formation of hydrogen peroxide which can be determined by anodic oxidation at a fixed potential. 

Depending on the immobilization procedure the enzyme microenvironment can also be modified significantly and the biocatalyst properties such as selectivity, pH and temperature dependence may be altered for the better or the worse. Mass-transfer limitations should also be accounted for particularly when the increase in the local concentration of the reaction product can be harmful to the enzyme activity. For instance H2O2, the reaction product of the enzyme glucose oxidase, is able to deactivate it. Operationally, this problem can be overcome sometimes by co-immobilizing a second enzyme able to decompose such product (e.g. catalase to destroy H202). 

Application of transition metal hexacyanoferrates for development of biosensors was first announced by our group in 1994 [118]. The goal was to substitute platinum as the most commonly used hydrogen peroxide transducer for Prussian blue-modified electrode. The enzyme glucose oxidase was immobilized on the top of the transducer in the polymer (Nation) membrane. The resulting biosensor showed advantageous characteristics of both sensitivity and selectivity in the presence of commonly tested reductants, such as ascorbate and paracetamol. 

X. Yang, L. Huaa, H. Gonga, and S.N. Tan, Covalent immobilization of an enzyme (glucose oxidase) onto a carbon sol-gel silicate composite surface as a biosensing platform. Anal. Chim. Acta 478, 67-75 (2003). 

Fig. 2. Effect of the number of immobilized enzyme layers on the enzyme activity. Purified (filled square) and non-purified (open square) anti-(glucose oxidase) Ig was used as a linker for immobilization of enzyme glucose oxidase, the activity of which was measured. (Reprinted with permission from [125])...

Fig. 3.13 A glucose biosensor based on CNTs (SWNT) and the enzyme glucose oxidase (in grey). Adapted by permission from Macmillan Publishers Ltd., [71], (2005).

The concentration of glucose in a blood sample, for example, can be measured using the enzyme, glucose oxidase, which catalyses, specifically, the oxidation of glucose ... 

Ambartsumian, T. G., Adamian, S. Y., Petrosia, L. S., and Simonian, A. L. (1992). Incorporation of water-soluble enzymes glucose-oxidase and urate oxidase into phosphatidylcholine liposomes. Biol. Membr, 5, 1878-87. 

A further approach to electrically wire redox enzymes by means of supramolecular structures that include CNTs as conductive elements involved the wrapping of CNTs with water-soluble polymers, for example, polyethylene imine or polyacrylic acid.54 The polymer coating enhanced the solubility of the CNTs in aqueous media, and facilitated the covalent linkage of the enzymes to the functionalized CNTs (Fig. 12.9c). The polyethylene imine-coated CNTs were covalently modified with electroactive ferrocene units, and the enzyme glucose oxidase (GOx) was covalently linked to the polymer coating. The ferrocene relay units were electrically contacted with the electrode by means of the CNTs, and the oxidized relay mediated the electron transfer from the enzyme-active center to the electrode, a process that activated the bioelectrocatalytic functions of GOx. Similar results were observed upon tethering the ferrocene units to polyacrylic acid-coated CNTs, and the covalent attachment of GOx to the modifying polymer. 

Fig. 7.116. Oxidation of glucose mediated by the enzyme glucose oxidase. The catalytic activity produces electrons and oxygen is reduced on the enzyme to produce H202, which is then electrochemically analyzable. In this way, glucose can be indirectly monitored. (Reprinted from F. A. Armstrong, H. A. O. Hill, and N. J. Walton, Acc. Chem. Res. 21 407, Fig. 1, copyright 1989, American Chemical Society.)...

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