Enzyme electrodes glutamate

N.F. Almeida and A.K. Mulchandani, A mediated amperometric enzyme electrode using tetrathiafulvalene and L-glutamate oxidase for the determination of L-glutamic acid, Anal. Chim. Acta, 282(2) (1993) 353-361. 

Recently, selective oxidases for L-lysine (EC 1.4.3.-) (Romette et al., 1983) and L-glutamate (EC 1.4.3.11) have been employed in enzyme electrodes. Wollenberger et al. (1989) developed a sensor based on glutamate oxidase from Streptomyces endus, which permits selective measurement of glutamic acid between 1 pmol/1 and 1 mmol/1 with a sample frequency of 120/h. In contrast, a sensor using an analogous... 

As early as 1975, Ahn et al. developed an enzyme electrode for glutamate composed of L-glutamate decarboxylase (EC 4.1.1.15) and a carbon dioxide sensor. 

Figure 1 Enzymes as signal transdncers. As drawn, an enzyme specific for only one substrate is immobilized in close proximity to the electrode surface. The substrate (e.g., glutamate) is oxidized by the enzyme to the corresponding enzyme product (e.g., a-ketoglu-tarate) with concurrent rednction of a cofactor in a 1 1 ratio. (NAD" is rednced to NADH for dehydrogenase enzymes, and molecular oxygen is reduced to peroxide in the case of oxidase enzymes.) Of the fonr species present in solution, only the product of the cofactor reduction (NADH or H2O2) is electrochemically active and produces an analytical signal, so the enzyme substrate (glutamate in this example) is transduced to an electroactive species by the enzyme. Barring introduction of NADH (or peroxide) to the solntion, any increase in faradaic cnrrent may then be attributed to the presence of the enzyme snbstrate alone.

Yao, T., N. Kobayashi, and T. Wasa. 1990. Flow-injection analysis for L-glutamate using immobilized L-glutamate oxidase Comparison of an enzyme reactor and enzyme electrode. Anal. Chim. Acta 231 121—124. 

When the sample solution containing glutamic acid was injected into the system, the potential of the carbon dioxide gas-sensing electrode increased with time. The enzyme reaction was carried out at pH 4.4, which was sufficiently below the pK value (6.34 at 2 fc) of carbon dioxide. 

Thus, the enzyme can be coupled to ammonia electrodes, field effect transistors or chemical methods of ammonia determination [115]. Alternatively, a bi-enz5mie system can be applied combining glutaminase with glutamate oxidase (Eq. (11.4)) ... 

The electrochemical detection utilized the re-oxidation of hexacyano-ferrate(II) on a platinum electrode. For pyruvate determination this assay was extended to a 3-enzyme system by the addition of glutamate p5u-uvate transaminase, which produces alanine from pyruvate. All enz5unes were used in solution in a reaction chamber of approximately 2 pi directly in front of the electrode. The cofactor NAD" " was coupled to dextran with a molecular weight of 40,000 to avoid its replacement for each assay. As the sensor responded to L-alanine and pyruvate again a differential measurement was required when a sample contained both compounds. It was applied to off-line monitoring of a cultivation of S. cerevisiae and data showed good correlation to the photometric assays. 

One of the first attempts to measure this metabolite in the brain was carried out by Zilka et al. [139] using microdialysis coupled to an electrochemical flow cell with the immobilized enzyme glutamate oxidase (GIOD). To avoid the interference of endogenous electroactive compounds, a film of 1,2 diaminobenzene was electropolymerized onto the Pt working electrode. 

These ferrocene modified polysiloxane polymers were also used to construct glycolate [6,7], lactate [7], acetylcholine [12,81], glutamate [12] and cholesterol [81] sensors. All these electrodes showed that ferrocene containing siloxane polymers efficiently shuttled electrons between redox center(s) of enzyme and the electrode surface. 

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