Glucose oxidase catalytic reaction

Enzymes are proteins of high molecular weight and possess exceptionally high catalytic properties. These are important to plant and animal life processes. An enzyme, E, is a protein or protein-like substance with catalytic properties. A substrate, S, is the substance that is chemically transformed at an accelerated rate because of the action of the enzyme on it. Most enzymes are normally named in terms of the reactions they catalyze. In practice, a suffice -ase is added to the substrate on which die enzyme acts. Eor example, die enzyme dial catalyzes die decomposition of urea is urease, the enzyme dial acts on uric acid is uricase, and die enzyme present in die micro-organism dial converts glucose to gluconolactone is glucose oxidase. The diree major types of enzyme reaction are ... 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

Experience shows that flow microcalorimetry is a universal technique that is suitable for the investigation of the catalytic properties of immobilized biocatalysts. This review has summarized all basic examples of its application, but has not exhausted all of their potential possibilities. As an example, the steady-state measurement of a bi-substrate enzyme reaction with a co-immobilized glucose oxidase-catalase system was reported [26]. However, there is no report on the evaluation of kinetic properties of partial enzymes in co-immobilized systems. Even the measurement of the overall heat produced in such systems does not provide direct information about partial reactions. We believe that new approaches to analyze these systems based on mathematical modeling can be developed. 

Purification and catalytic reaction of glucose oxidase A. niger GOase may be obtained commercially at low prices. However, if desired, crude preparations of this enzyme may be purified as described by Nakamura and Fujiki (1968). 

GC mode experiments have been applied to the study of immobilized oxi-doreductases such as diaphorase and the glucose oxidase/glucose system (15,21), which has also been investigated by feedback with ferrocenyl mediators (10). In the feedback experiment, the catalytic cycle of the enzyme is dependent on ferrocenium species generated at the tip, as described in Sec. I.C. A generation-collection experiment utilizes a bulk solution concentration of the oxidized mediator, and the tip is poised at a potential sufficiently positive to detect ferrocene, or another reaction product such as H202, present near the interface (Fig. 6). The enzymatic reaction therefore occurs over the whole specimen, wherever there is active enzyme and a supply of substrate. In the feedback experiment, the tip current includes the flux of mediator from bulk solution as well as the flux of reduced mediator due to... 

In order to determine, the quantity of enzyme which had been covalently immobilized onto the beads, calibration curves relating enzyme activities to enzyme concentrations were prepared. Various concentrations of each enzyme (glucose oxidase and peroxidase) were employed in these calibrations. O-Dianisidine was used as an enzyme reactant. The appearance of absorbency due to the oxidation of 0-dianisidine at 460 nm, by the catalytic activity of the enzymes, was followed with the help of the Bausch Loads, Double Beam, Spectronic 2000 spectrophotometer. The rate of reaction increased with the increased amount of enzyme entployed. 

The direct measurement of analyte concentrations below approx. 10 mol/L with electrochemical sensors is so far only possible with the advanced microfabrication process of Ikarijama et al. [21-23]. Usually a chemical amplifier system has to be used for increased sensitivity. The only analytes which already provide this amplification system themselves are enzymes catalytically turning over their substrates. If the product of the enzymatic reaction can be assayed with a sensor, the activity of the respective enzyme can also be determined. As an example, an amperometric assay for glucose oxidase using benzoquinone as an oxidant has been published [37] ... 

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