Enzyme electrodes arginine

Bacterial electrodes [11, 31, 33, 46, 48, 49, 60] In this type of electrode, a suspension of suitable bacteria is placed between the sensor proper and a dialysis membrane that prevents passage of high-molecular substances (see fig. 8.3). The sensor is usually a gas probe. In the simple types of bacterial electrode, the determinand is converted by a suitable strain of bacteria into a product sensed by the gas probe. Thus it is possible to determine arginine [46], glutamine [48],/.-aspartic acid [31],/.-histidine [60] and nitrate [33]. Hybrid bacterial - enzyme electrodes contain both a bacterial strain and a suitable enzyme. For example, an extract from ivingas Neurospora chossa can be used as a source of NAD nucleosidase and an Escherichia coli culture as a source of nicotinamide deaminase, so that the electrode responds to NAD [49] as a result of the series of reactions... 

Due to their response mechanism the polyion-selective electrodes are not sensitive to the small fragments of polyionic macromolecules. Thus, if an enzyme cleaves the polyionic molecule these sensors can be used for detection of enzyme activity. Polycation protamine is rich in arginine residues that make it a suitable substrate for protease-sensitive electrochemical assays. Real-time detection of trypsine activity was demonstrated with the protamine-selective electrode as a detector [38],... 

A coating bearing one enzyme (papain) is produced on the surface of a glass pH electrode by the method previously introduced (co-crosslinking). The papain reaction decreases the pH, and the pH-activity variation gives an autocatalytic effect for pH values greater than the optimum under zero-order kinetics for the substrate (benzoyl arginine ethyl ester) the pH inside the membrane is studied as a function of the pH in the bulk solution in which the electrode is immersed. A hysteresis effect is observed and the enzyme reaction rate depends not only on the metabolite concentrations, but also on the history of the system. 

Applications. A biotinylated GOX-based biosensor was developed based on a new electropolymerized material consisting of a pol3rp3uidyl complex of ruthenium(II) functionalized with a pyrrole group [90]. Because histidine, lysine and arginine functions also coordinate Os /Os , biosensors based on co-electrodeposited GOX, HRP, soybean peroxidase (SBP) and laccase with redox Os /Os polymer have been developed [89]. A metal chelate formed by nickel and nitrilotriacetic acid was used to modify a screen-printed electrode surface. The functionalized support allowed stable attachment of acetylcholinesterase and the resulting biosensor was used for sensitive detection of organophosphorus insecticides [91]. This method is attractive because it ensures a controlled and oriented enzyme immobilization, considerably improving the sensitivity and the detection limit. 

The second enzyme reaction (Eq. (41)) produces an electroactive product whose concentration is related to the content of arginine. Other hybrid electrodes have been constructed, for instance, for the determination of phosphate and fluoride [164]. 

The earhest example of a membrane-enzyme oscillator was presented by Na-parstek, Caplan, and coworkers [52]. This oscillator consists of papain immobilized in a porous collodion membrane that is permeable to water, substrate, and ions. The membrane is cast as a thin film against a pH electrode and is exposed to an alkaline (pH 10) external solution of benzyl arginine ethyl ester (BAEE), which is a substrate... 

The amino acid biosensor response is expressed in terms of the partial pressure of oxygen and varies with the nature of the amino acid concerned. Figure 4.29 shows the activity of the enzyme towards each amino acid and, consequently, demonstrates the non-specificity of the sensor. An electrode that uses L-lysine a-oxidase for the determination of L-lysine, for example, is also sensitive to L-omithine, L-arginine, and L-phenylalanine [179]. Only electrodes that use decarboxylases give good specificity (see 4.4.3.c). 

This is normal for microorganisms that contain a number of enzymatic systems. A pNHa electrode with immobilized Streptococcus faecium detects arginine through the presence of three enzymes [60], which catalyse successively the following reactions ... 

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