Lactate oxidase, reactions involving

Amplification of the sensitivity of substrate or co-en me recycling is especially efficient in thermometric analysis since all the reactions involved frequently contribute to increasing the overall temperature change. One case in point is the determination of lactate or pyruvate by substrate recycling using co-immobilized lactate oxidase and lactate dehydrogenase [160]. 

Figure 22.5 An example of reactions involved in an enzyme-catalyzed recycling processes for amplification of the sensitivity. In the left part (A) of the figure the enzyme-pair hexokinase and pyruvate kinase is used for recycling of the coenzyme ATP/ADP. In the right part (B), substrate recycling of pymvate or lactate is accomplished using the enzyme-pair lactate oxidase/lactate dehydrogenase. A multiplication effect is obtained by combination of A and B resulting in a very high sensitivity [27], The calorimetric sensitivity is further inreased by including catalase (cat).

Examples of enzymes used for biosensors include glucose oxidase for glucose sensors, alcohol oxidase for ethanol sensors, lactate oxidase for lactate sensors and urease for urea sensors. A typical enzyme reaction, as described by equation 5.2 might involve the transfer of an electron, a pH change, hydrolysis, esterification or bond cleavage. The type of enzymatic reaction that occurs determines the type of transducer that is used. 

Several flow strategies involving enzymatic reactions have been applied for determination of LA in food and beverages. Most of the work to be explored in this chapter involves the catalytic action of lactate dehydrogenase (LDFl) and lactate oxidase (LOD) in the conversion of LA into pyruvic acid (Figure 12.2). LDH requires a biological redox... 

L-Amino acid oxidase has been used to measure L-phenylalanine and involves the addition of a sodium arsenate-borate buffer, which promotes the conversion of the oxidation product, phenylpyruvic acid, to its enol form, which then forms a borate complex having an absorption maximum at 308 nm. Tyrosine and tryptophan react similarly but their enol-borate complexes have different absorption maxima at 330 and 350 nm respectively. Thus by taking absorbance readings at these wavelengths the specificity of the assay is improved. The assay for L-alanine may also be made almost completely specific by converting the L-pyruvate formed in the oxidation reaction to L-lactate by the addition of lactate dehydrogenase (EC 1.1.1.27) and monitoring the oxidation of NADH at 340 nm. 

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