Enzyme glucose monitoring

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. 

Possibilities for Enzymes in Implantable Fuel Cells There is significant and increasing demand for power supplies for implantable medical devices, including continuous glucose monitors for diabetic patients, thermal sensors for... 

The importance of having adequate supplies of NADPH for the regeneration of these various enzymes cannot be over emphasized. In normal situations this cofactor can be adequately provided by the reductive pentose phosphate pathway. Monitoring the activity of the pentose phosphate pathway has been proposed as a unique way to study the metabolic response to oxidative stress, since the glutathione peroxidase activity is coupled via glutathione reductase to the enzyme glucose-6-phosphate dehydrogenase (Ben Yoseph et ah, 1994). 

Another enzyme used for the measurement of glucose is hexokinase (EC 2.7.1.1) which catalyses the phosphorylation of glucose to produce glucose-6-phosphate with adenosine triphosphate as the phosphate donor and magnesium ions as an activator. The rate of formation of glucose-6-phosphate can be linked to the reduction of NADP by the enzyme glucose-6-phosphate dehydrogenase (EC 1.1.1.49). This indicator reaction can be monitored spectrophotometrically at 340 nm or fluorimetrically ... 

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.)...

One problem with early glucose monitors is that their response depended on the concentration of 02 in the enzyme layer, because 02 participates in Reaction 17-10. If the 02 concentration is low, the monitor responds as though the glucose concentration were low. 

In the earlv 1960s. a promising approach to glucose monitoring was rlcreloped in the form of an enzyme electrode lhal used oxidation of glucose by the enzyme GOD, This approach has been incorporated into a leu clinical analyzers lor blood glucose determination... 

The clinical utility of electrochemical sensors for continuous glucose monitoring in subcutaneous tissue has been limited by numerous challenges related to sensor component and biocompatibility-based failures.1,2 Sensor component failures include electrical failure, loss of enzyme activity, and membrane degradation,3 4 while examples of biocompatibility-based failures include infection, membrane biofouling (e.g., adsorption of small molecules and proteins to the sensor surface), and bbrous... 

Zimmermann, S., Fienbork, D., Wasilik, M., Liepmann, D., A novel in-device enzyme immobilizatoin method for BIOMENS, demonstrated for a continuous glucose monitor. Micro Total Analysis Systems 2000, Proceedings pTAS 2002 symposium, 6th, Nara, Japan, Nov. 3-7, 2002, 449M51. 

During the past 40 years there have been numerous exciting extensions of electrochemistry to the field of analytical chemistry. A series of selective-ion potentiometric electrodes have been developed, such that most of the common ionic species can be quantitatively monitored in aqueous solution. A highly effective electrolytic moisture analyzer provides continuous online assays for water in gases. Another practical development has been the voltammetric membrane electrode for dioxygen (02), which responds linearly to the partial pressure of 02, either in the gas phase or in solution. The use of an immobilized enzyme (glucose oxidase) on an electrode sensor to assay glucose in blood is another extension of electrochemistry to practical analysis. 

A great number of enzymes have already been combined with electrodes. In some cases, several possible enzymatic routes may be selected, depending on the substrate to be analyzed. One such example is that used to determine aspartame (Fig. 3) (18-20). Enzyme electrodes use, ideally, only one enzyme and monitor the main substrate-enzyme reaction, for example, glucose oxidase-glucose. If the main substrate-enzyme reaction is not electrochemically detectable or if signal amplification is required, bi- or trienzymatic sequences may be applied. 

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