Alanine sensor

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. 

At a later stage, Girotti et al. developed a highly sensitive and rapid bioluminescence flow-through sensor for the determination of the L-phenyl-alanine (Phe) in serum by monitoring the reduced form of nicotinamide... 

Fig.4 The principle of chiral recognition by gas sensors chiral discrimination by preferential sorption of the enantiomers of N-TFA-alanine methyl ester (N-TFA-Ala-OMe) into enantioselective (R)- and (S)-octyl-Chirasil-Val polymers. The chemical information is transformed into optical signals by the respective transducers...

Several sensors for L-alanine are obtained by immobilizing L-alanine dehydrogenase over an ammonia gas-sensing electrode (288) or over an O2 sensor (280). The enzyme catalyzes the specific deamination of alanine in the presence of the coenzyme NAD ... 

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. 

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. 

Tanaka K, Inoue S, Nagase H, Takamura Y, Niijima A. 1990. Amino acid sensors sensitive to alanine and leucine exist in the hepato-portal system in the rat. J Auton Nerv Syst 31 41-46. 

The following substrates can be determined with almost identical sensitivity by using D-amino acid oxidase in combination with an ammonium ion sensitive electrode D-alanine, D-leucine, D-norleucine, D-methionine, and D-phenylalanine. L-amino acid oxidase sensors have been described for L-leucine, L-cysteine, L-methionine, L-tryptophan, and L-tyrosine (Guilbault and Hrabankova, 1971), and L-histidine and L-arginine (Tran-Minh and Broun, 1975). 

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.

The determination of alanine aminopeptidase (AAP, EC 3.4.11.14) is of importance in the rapid diagnosis of liver and bile diseases. Common assays involve the coupling of alanine hydrazide cleavage with a chro-mogenic reaction. Kirstein (1987) proposed indicating the rate of hydrazine formation electrochemically. In contrast to an amperometric urea sensor based on this indication method (see Section 3.1.21), the pH value in the near-electrode space remains unchanged while the concentration of electrode-active hydrazine rises. The incubation period for AAP assay is lowered to half of that needed in the conventional method, the two correlating with r = 0.994. 

Hyun and coworkers reported fluorescent anion sensors 21 and 22 for recognition of AI-Boc or 3,5-dinitrobenzoyl (DNB) protected a-amino acids (Fig. 12). Amino acid such as alanine (Ala), valine (Val), threonine... 

Aspartate transaminase (AST) or the equivalent serum glutamic oxaloacetic transaminase (SGOT) and alanine transaminase (ALT) or the equivalent serum glutamic pyruvic transaminase (SGPT) are useful indicators of liver conditions such as alcoholic liver disease (Cohen and Kaplan, 1979). A multiplexed, paper-based microfluidic assay designed for quick, semiquantitative measurement of AST and ALT in a hn-ger-stick specimen has been tested clinically (Pollock et al., 2012). Such paper-based techniques have also been supplemented by optical detection (Swanson et al., 2015). Microfluidic channels combined with electrochemical sensors have also used to measure ALT and AST (Song et al., 2009). 

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