Lactate/pyruvate substrate recycling

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]. 

The use of alkaline phosphatase as an enzyme label allows enhancement of the sensitivity by using phosphoenolpyruvate as substrate and the utilization of a separate detection column in the ET unit for the determination of the product (pyruvate) by substrate recycling. This is accomplished by using the substrate recycling system described above [18] comprising the coimmobilized enzymes lactate dehydrogenase (reduces pyruvate to lactate under the consumption of... 

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).

Figure 10.14 Substrate recycling of lactate/pyruvate in PANI/LOD-LDH electrodes...

In a sensor for lactate a bienzyme system composed of cytochrome 62 for lactate oxidation to pyruvate, and lactate dehydrogenase for conversion of pyruvate back to lactate has been used [321]. Hexacyanoferrate(III) served as electron acceptor for cytochrome b2- The reduced mediator was reoxidized at the electrode, thus giving a measuring signal depending on the analyte concentration. Attempts to determine both substrates of the recycling system have shown that, at tenfold amplification for lactate, the sensitivities for lactate and pyruvate are almost identical. The same recycling scheme has also been used in connection with Fe-EDTA as electron mediator in place of hexacyanoferrate(III) [336]. 

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