Glucose oxidase, selectivity

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). 

E. Csoregi, D.W. Schmidtke, and A. Heller, Design and optimzation of a selective subcutaneously implantable gluocse electrode based on wired glucose oxidase. Anal. Chem. 67, 1240-1244 (1995). 

J. Wang and H. Wu, Highly selective biosensing of glucose utilizing a glucose oxidase + rhodium + Nafion biocatalytic-electrocatalytic-permselective surface microstructure. J. Electroanal. Chem. 395, 287-291 (1995). 

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. 

Figure 6.30 Schematic representation of a glucose sensor operating by diffusion across a perm-selective membrane (as represented by the vertical arrows) GOD is glucose oxidase.

Examples of surface-immobilized mediators are electropolymerized azines for electro-oxidation of The extreme form of this approach is formation of biocatalytic monolayer, comprising a surface-bound mediator species that is itself bound to a single enzyme molecule. Katz et al. report a complete cell based on novel architecture at both electrodes (Figure 7). On the anode side, the FAD center of glucose oxidase is removed from the enzyme shell and covalently attached to a pyrroloquinoline quinone (PQQ) mediator species previously immobilized on a gold surface. The GOx apoenzyme (enzyme with active center removed) is reintroduced in solution and selectively binds to FAD, resulting in a PQQ-... 

Fig. 8.4 (a) In the presence of oxygen, the glucose oxidase-catalyzed oxidation of y -D-glucose leads to the formation of gluconolactone. (b) Carboxypeptidase A selectively cleaves the substrate, hippuryl-L-phenylalanine, thus leading to the formation of hippuric acid and phenylalanine. 

Selected entries from Methods in Enzymology [vol, page(s)j Detection and quantification, 74, 608-616 effect of antigen/anti-body ratio, 74, 613, 614 applications, 74, 614-615 controls, 74, 612 data analysis, 74, 612-613 immunoglobulin G [conjugation to glucose oxidase, 74, 610 heat aggregation, 74, 609-610 heat denaturation, 74, 610 immobilization, 74, 610] precision, 74,... 

Electrodes based on enzyme activity. These are selective and sensitive devices that may be used to measure substrate concentrations. A biosensor based on glucose oxidase is used to measure the concentration of glucose by detecting the production of H202. 

This is the reaction taking place at the surface of the thermal sensor, the pellistor, discussed in Chapter 3. An example of a biocatalyst is the enzyme glucose oxidase (GOD) which highly selectively promotes oxidation of D-glucose to gluconic acid. 

For this type of sensor, a catalase-free glucose oxidase must be used. In such a case, the hydrogen peroxide produced by the reaction with oxygen remains in the selective layer and can be detected by oxidation according to the reaction... 

The feasibility of amperometric sucrose and mercury biosensors based on the immobilization of invertase, glucose oxidase, and muta-rotase entrapped in a clay matrix (laponite) was investigated by Mohammadi et al. [31]. In this work, the effect of pH of a tri-enzymatic biosensor in which the optimum pH of the three enzymes is different (Invertase, pH 4.5 Glucose oxidase, pH 5.5 and Mutarotase, pH 7.4) [41] was studied. The pH effect on the biosensor response was analyzed between pH 4 and 8 and the highest activity was found at pH 6.0. In order to improve the selectivity of the invertase toward mercury and to avoid silver interference, a medium exchange technique was carried out. The biosensor was exposed to mercury in an acetate buffer solution at pH 4 while the residual activity was evaluated with phosphate buffer solution at pH 6 [41]. 

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