Alkaline phosphatase 4-aminophenol product

The GC mode can also be used to image some enzymes that are not oxidoreductases. For the important enzymes alkaline phosphatase (ALP) and galactosidase, this has been achieved by using an enzyme substrate that is not redox active at the UME potential, whereas one of the products (p-aminophenol (PAP)) can be oxidized. The experiment is detailed in the Protocol P2 H37. The use of potentiometric probes is also possible. Table 37.2 provides an overview about the investigated enzymes. 

Alkaline phosphatase is one of the most suitable enzymes for electrochemical immunoassays owing to its high turnover number and broad substrate specificity. Different substrates have been used, but 4-aminophenyl phosphate is most suitable, since the reaction product, 4-aminophenol is easily oxidized without fouling of the electrode surface. Thyroxine-binding globulin, cortisol, and prostatic acid phosphatase have been detected by using alkaline phosphatase. 

GC mode SECM experiments have been used to detect localized activity of a variety of enzymes (see Table 11.2). Since microelectrodes are used in the life sciences to detect neurotransmitters [43], metal cations [44], and free radicals [45], a wide variety of probes may be combined with SECM positioning technology to obtain spatially resolved information. The GC mode experiments may be carried out with potentiometric or amperometric tips depending on the species to be sensed. The tip must be chosen to determine a product or reactant consumed by the enzyme reaction, for example, H for inunobilized urease, H2O2 for immobilized GOx, or p-aminophenolate for alkaline phosphatase (ALP). A list of enzymes and the tips anployed is given in Table 11.2. In addition to the enzymes listed, similar strategies have been employed for tissues and cells in order to... 

The enzyme labels are typically horse radish peroxidase (HRP, electrochemical detection shown in the scheme) and alkaline phosphatase (ALP). Lor ALP, the selection of substrates is limited and p-aminophenyl phosphate (PAPP) is mostly used as the resulting aminophenol becomes easily and reversibly oxidised at the electrode. A wide choice of substrates (DH2) generating electroactive products includes hydroquinone, tetramethylbenzidine, aminosalicylic acid and iodide in the case of HRP ... 

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