Oxidase enzymes reactions

Electrochemical analyzers based on the amperometric measurement of oxygen are used to measure the rate of oxidase enzyme reactions. For example, the substrate glucose is determined by measuring the rate of oxygen consumption in the presence of glucose oxidase. Results are obtained in less than a minute. Similarly,... 

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 ... 

Several biosensors are commercially available. One of the most useful is the glucose sensor. The standard sensor determines glucose concentration based on the glucose oxidase enzyme. The chemical reaction for oxidation of glucose is ... 

Enzyme-coupled ECL enables the selective determination of many clinical analytes that are not in themselves directly electrochemiluminescent, but that can act as substrates for a variety of enzymic reactions. There are two general strategies for ECL the use of dehydrogenase enzymes, which convert NAD+ to NADH, and oxidase enzymes, which produce hydrogen peroxide. 

Hydrogen peroxide produced as a result of reactions of oxidase enzymes with analyte substrates can be sensitively determined, both directly by luminol ECL and indirectly by Ru(bpy)32+ ECL. For the latter, hydrogen peroxide is detected on the basis of its ability to diminish the ECL reaction between Ru(bpy)32+ and added oxalate, by reacting with, and depleting the concentration of, oxalate. Thus ECL intensity is inversely proportional to the concentration of analyte. This principle has been used, for example, to determine cholesterol [70],... 

A number of autoxidation reactions exhibit exotic kinetic phenomena under specific experimental conditions. One of the most widely studied systems is the peroxidase-oxidase (PO) oscillator which is the only enzyme reaction showing oscillation in vitro in homogeneous stirred solution. The net reaction is the oxidation of nicotinamide adenine dinucleotide (NADH), a biologically vital coenzyme, by dioxygen in a horseradish peroxidase enzyme (HRP) catalyzed process ... 

Environmental agents that influence microsomal reactions will influence hexachloroethane toxicity. The production of tetrachloroethene as a metabolite is increased by agents like phenobarbital that induce certain cytochrome P-450 isozymes (Nastainczyk et al. 1982a Thompson et al. 1984). Exposure to food material or other xenobiotics that influence the availability of mixed function oxidase enzymes and/or cofactors will change the reaction rate and end products of hexachloroethane metabolism and thus influence its toxicity. 

Fig. 19 Reaction scheme of the electron transfer type of oxidase enzyme senser...

FIGURE 5.7. Effect of changing the cosubstrate and the pH on the kinetics of an homogeneous redox enzyme reaction as exemplified by the electrochemical oxidation of glucose by glucose oxidase mediated by one-electron redox cosubstrates, ferricinium methanol ( ), + ferricinium carboxylate ( ), and (dimethylammonio)ferricinium ( ). Variation of the rate constant, k3, with pH. Ionic strength, 0.1 M temperature 25°C. Adapted from Figure 3 in reference 11, with permission from the American Chemical Society. 

In order to follow the progress of an enzyme-catalysed reaction it is necessary to measure either the depletion of the substrate or the accumulation of the product. This demands that either the substrate or the product show some measurable characteristic which is proportional to its concentration. This is not always the case and a variety of techniques have been developed in order to monitor enzyme reactions. In order to illustrate some of the methods and also to give an appreciation of the technical details and the calculations, three examples are given (Procedures 8.4 to 8.6) that use the enzyme D-amino acid oxidase (Table 8.4). 

The CYP enzymes active in phase I reactions are often oxidases or hydroxylases, sometimes called mixed function oxidase (MFO). An oxidase enzyme introduces into the substrate (i.e. the unwanted compound) both atoms of an oxygen molecule whilst... 

Many natural products are produced by the coupling of two or more phenolic systems, in a process readily rationalized by means of radical reactions. The reactions can be brought about by oxidase enzymes,... 

Thus, the oxidase-substrate reaction yields oxidized substrate and inactive reduced enzyme the enzyme is returned to its active state by electron transfer, producing hydrogen peroxide. The peroxidase converts the peroxide, generating an electrochemical signal in the electrode. 

Figure 4. Linearity of the metabolism of parathion and benzphetamine by a reconstituted monooxygenase oxidase enzyme system from rabbit liver. The 0.5-mL reaction mixture contained 50 fig of sodium deoxycholate, 15 iig of dilauroyl l-5-phosphatidylcholine, 1.5 units of NADPH-Cytochrome c reductase, 0.5 nmol of Cytochrome P-450, 0.05M Hepes buffer (pH 7.8), 0.015M MgCh, O.lmU EDTA, and 5 X lO M [ethyl- C] parathion or / X 10 M benzphetamine.

---