Pyruvate Sensors

He X. Rechnitz G.A., Plant tissue-based pyruvate fiberoptic sensor, Anal. Chim. Acta 1995 316(1) 57-63. 

Y. Inaba, K. Mizukami, N. Hamada-Sato, T. Kobayashi, C. Imada and E. Watanabe, Development of a D-alanine sensor for the monitoring of a fermentation using the improved selectivity by the combination of d-amino acid oxidase and pyruvate oxidase, Biosens. Bioelectron., 19(5) (2003) 423-431. 

Revzin A, Sirkar K, Pishko M. Glucose, lactate, and pyruvate biosensor arrays based on redox polymer/oxidoreductase nanocomposite thin films deposited on photo-lithographically patterned gold electrodes. Sensors and Actuators B 2002, 81, 359-368. 

Biosensors based on carbon fiber ultramicroelectrodes have been used to determine pyruvate (2) and glucose (3). Glucose sensors using platinum ultramicroelectrodes have also been reported (4), including the entrapment of glucose oxidase in an electropolymerized film of polyaniline (5,6). Ikariyama and co-workers have used platinum ultramicroelectrodes modified with platinum black to construct very sensitive glucose sensors (7-13). 

Sensors have also been constructed from some oxidases directly contacted to electrodes to give bioelectrocatalytic systems. These enzymes utilize molecular oxygen as the electron acceptor for the oxidation of their substrates. Enzymes such as catechol oxidase, amino acid oxidase, glucose oxidase, lactate oxidase, pyruvate oxidase, alcohol oxidase, xanthine oxidase and cholesterol oxidase catalyze the oxidation of their respective substrates with the concomitant reduction of O2 to H2O2 ... 

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. 

To date various polymeric electron transfer systems have been incorporated to enzyme sensors for glucose, lactate, aldose, pyruvate, ascorbate, choline, acetylcholine, cholesterol, formaldehyde, phenoUcs, nitrate, sulfite and histamine. 

Scheller et al. reported amperometric pyruvate sensors by potentiostatic co-pol5nmerization of Os(bipy)2pyridineCl-modified pyrrole monomer and thiophene on platinized glassy carbon electrodes on which pyruvate oxidase was adsorbed [78]. This pol5dhiophene based redox pol5uner was reported to have excellent electron transfer properties with significantly improved stability compared with polypyrrole as they are not affected by oxygen [79]. However, notable interference by ascorbate needs to be eliminated. 

Gorton et al. reported carbon paste electrodes based on Toluidine Blue O (TBO)-methacrylate co-polymers or ethylenediamine polymer derivative and NAD" " with yeast alcohol dehydrogenase for the analysis of ethanol [152,153] and with D-lactate dehydrogenase for the analysis of D-lactic acid [154]. Use of electrodes prepared with dye-modified polymeric electron transfer systems and NAD+/NADH to detect vitamin K and pyruvic acid has also been reported by Okamoto et al. [153]. Although these sensors showed acceptable performances, insensitivity to ambient oxygen concentration, sensor stability and lifetime still need to be improved to obtain optimal dehydrogenase based enzyme biosensors. 

Substitution of other oxoreductase enzymes for glucose oxidase allows amperometric biosensors for other substrates of clinical interest to be constructed. Practical sensors with commercial application in critical care analyzers for blood lactate have been realized. Other amperometric biosensors reported include cholesterol, pyruvate, alanine, glutamate, and glutamine. By using the multiple enzyme cascade shown in the reactions below, an amperometric biosensor for creatinine is also possible. Electrochemical oxidation of H2O2 is the detection mechanism. 

Colorimetric and fluorimetric NH3 sensors contain mixtures of pH indicators having suitable dissociation constants at the tip of the fiber bundle. The measuring solution is separated from this indicator layer by an NH3 gas-permeable membrane covered by an immobilized de-aminating enzyme, e.g. urease (Wolfbeis, 1987 Arnold, 1987). The fluorimetric indication of NADH has been used in optical biosensors for lactate, pyruvate, and ethanol, where the respective dehydrogenase is immobilized at the tip of an optical NADH sensor (Arnold, 1987 Wangsa and Arnold, 1988). 

The different cosubstrate specificities of the lactate-oxidizing enzymes offer the use of a great variety of electrochemical indicator reactions in membrane sensors. In enzyme electrodes based on LDH the biochemical reaction has been coupled to the electrode via NADH oxidation, either directly or by using mediators or additional enzymes (see Section 3.2.1). This leads to a shift of the unfavorable reaction equilibrium by partial trapping of the reduced cofactor. Such a shift has also been achieved by using pyruvate oxidase coimmobilized with LDH (Mizutani, 1982). 

The LMO sensor has also been applied to the sequential determination of lactate and LDH activity. When the current decrease resulting from lactate oxidation was complete, NADH and pyruvate were added to the measuring cell. The subsequent current decrease reflects the lactate formation by the LDH-catalyzed reaction. The time required for one sequential measurement was 4 min. The CV for 20 LDH determinations was 1.2%. 

Pyruvate oxidase requires the presence of thiamine pyrophosphate (0.1 mmol/1) and Ca2+ (2.5 mmol/1) for maximum activity. It should be used in 40 mmol/1 Tris buffer, pH 6.5-7.5, containing 0.5 mmol/1 phosphate. At higher phosphate concentrations substrate inhibition occurs this effect has been utilized in a phosphate sensor based on immobilized PyOD (Tabata and Murachi, 1983). Since PyOD is relatively unstable, for biosensors the enzyme has been immobilized by physical entrapment in, e.g., collagen (Mizutani et al., 1980), poly(vinyl chloride) and acetylcellulose (Kihara et al., 1984a,b). 

Mascini and Mazzei (1986) succeeded in the covalent immobilization of PyOD to a Biodyne Immunoaffinity Membrane (Pall Biodyne, USA) containing carboxylic groups on the surface. The membrane was preactivated with a carbodiimide derivative. The enzyme membrane was fixed on the tip of a hydrogen peroxide-indicating Pt electrode between a cellulose acetate membrane and a further dialysis membrane. This pyruvate sensor has been applied to serum measurement. Over 30 days the sensitivity dropped by only 13%. 

The LDH sensors described in Section 3.1.4 can also be used for pyruvate measurement. Since the equilibrium of the LDH reaction lies far to the product side no trapping of lactate or NAD+ is necessary. On the other hand, no indicator reactions that consume NADH within the enzyme layer can be applied, such as reaction with NMP+ or HRP. However, some pyruvate sensors utilizing the signal formed by anodic... 

Suaud-Chagny and Goup (1986) immobilized LDH on a pyrolytic carbon fiber microelectrode by impregnation in an inert protein sheath that was first electrochemically deposited around the active tip of the electrode. The NADH detection was improved by electrochemical treatment of the electrode. The detection limit for pyruvate was lower than 1 pmolA. The sensor was used to estimate pyruvate concentration in rat cerebrospinal fluid. 

With a constant of K = 2.7640-5 mol/1 (pH 7.0, 25°C) the equilibrium of the LDH-catalyzed reaction lies far to the lactate side. This means that whereas for lactate sensors based on LDH the forward reaction has to be forced by alkaline buffer and pyruvate- or NADH-trapping agents, the reduction of pyruvate proceeds spontaneously under normal conditions. This direction of the reaction has been used in a sequence electrode for pyruvate assay (Weigelt et al., 1987b). In the presence of lactate monooxygenase (LMO) lactate formed from pyruvate by LDH is oxidized by molecular oxygen, the consumption of which was indicated at a Clark-type electrode. The enzymes were immobilized in a gelatin membrane. Of course such a sensor measures the concentration of lactate in the sample, too. Therefore it is suited to the determination of the lactate/pyruvate ratio, which is a clinically important parameter. Pro-... 

Fig. 85. Calibration curves of an LDH-LMO sensor for lactate ( ) and pyruvate (X). (Redrawn from Weigelt et al., 1987b).

The lactate oxidation catalyzed by LMO forms the basis of several other multienzyme electrodes (Fig. 86). The LDH-LMO sensor has also been used to assay the activity of alanine aminotransferase (ALAT, EC 2.6.1.2) and pyruvate kinase (PK, EC 2.7.1.40) (Weigelt 1987 Weigelt et al., 1988). The sample was added to the NADH-containing measuring solution and when the steady state signal for endogenous lactate and pyruvate was attained the substrates of the enzyme to be determined... 

Fig. 86. Coupling of enzyme reactions for the design of a sensor family based on LMO. CK = creatine kinase, PK = pyruvate kinase, MDH = malate dehydrogenase, PEP = phosphoenolpyruvate, ALAT = alanine aminotransferase, ASAT = aspartate aminotransferase.

Fig. 87. Response curve of the sequential determination of lactate, pyruvate, and creatine kinase activity with a LMO-LDH-PK sensor. CP = creatine phosphate, lactate 3.4 mmol/1, pyruvate 245 pmol/1, CK 504 U/l.

Fig. 102. Schematic representation and measuring curves of a recycling sensor for ADP and ATP with pyruvate measurement via the sequence lactate dehydrogenase-lactate monoxygenase. PEP = phosphoenolpyruvate. (Redrawn from Wollenberger et al., 1987a).

The principle of enzymatic amplification can be drastically simplified by conducting the two partial reactions of the cycle with only one enzyme. Using this approach, Schubert et al. (1990) developed an LDH sensor for NADH determination. The enzyme was immobilized in a gelatin membrane and coupled to an oxygen probe, where it catalyzes the oxidation of NADH by pyruvate ... 

Burstein et al. (1986) have shown that in addition to induction and inhibition mechanical and chemical changes of the cell structure effect the selectivity of microbial sensors. Escherichia coli cells were treated by ultrasound, extrusion, or crosslinked with glutaraldehyde before used in sensors for D- and L-lactate, succinate, L-malate, 3-glycero-phosphate, pyruvate, NADH, and NAD PH. The treatment caused different selectivity of the respiratory chain and thus permitted an increase in the specificity of the respective sensors. 

Weigelt et al. (1987b) attempted the measurement of the lactate/py-ruvate ratio in plasma by using a lactate dehydrogenase-LMO sequence electrode. The sensor was connected to a pC>2 meter and was equally sensitive for lactate and pyruvate. Determination of concentrations of both substrates in a sample requires a time period of about 3 min. 

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