Alkaline phosphatase labeling

Chemiluminescence and bioluminescence are also used in immunoassays to detect conventional enzyme labels (eg, alkaline phosphatase, P-galactosidase, glucose oxidase, glucose 6-phosphate dehydrogenase, horseradish peroxidase, microperoxidase, xanthine oxidase). The enhanced chemiluminescence assay for horseradish peroxidase (luminol-peroxide-4-iodophenol detection reagent) and various chemiluminescence adamantyl 1,2-dioxetane aryl phosphate substrates, eg, (11) and (15) for alkaline phosphatase labels are in routine use in immunoassay analyzers and in Western blotting kits (261—266). 

Instead of immobilizing the antibody onto the transducer, it is possible to use a bare (amperometric or potentiometric) electrode for probing enzyme immunoassay reactions (42). In this case, the content of the immunoassay reaction vessel is injected to an appropriate flow system containing an electrochemical detector, or the electrode can be inserted into the reaction vessel. Remarkably low (femtomolar) detection limits have been reported in connection with the use of the alkaline phosphatase label (43,44). This enzyme catalyzes the hydrolysis of phosphate esters to liberate easily oxidizable phenolic products. 

Alkaline phosphatase-labeled probes are synthesized so that 18 bases are complementary to sequences on the arms of the bDNA. Three hybridization sites are located on each branch for a total binding capacity of 45 labeled probes per bDNA molecule. The alkaline phosphatase catalyzes the dephosphorylation of chemiluminescent substrate, dioxetane (Lumi-Phos Plus, Lumigen, Detroit, MI). The intensity of the light emission is measured with a plate luminometer as relative luminescent units. 

Indeed, a bDNA assay for diagnosis of African trypanosomiasis was developed and compared with buffy coat microscopy for detection of T brucei in human blood samples (Harris etal., 1996). Two repetitive DNA sequences found only in the T. brucei complex, a 177-bp satellite repeat and the ribosomal mobile element, were selected as targets in the bDNA assay. The assay used the standard bDNA components capture probes, target probes, amplifier molecules, and alkaline phosphatase-labeled probes. Various blood fractions and sample preparation methods were examined. Ultimately, buffy coat samples resulted in the highest sensitivity. Although typanosomes do not infect leukocytes, they cosediment with them. 

Kiyama, H., Emson, P.C., and Tokyama, M. (1992) In situ hybridization histochemistry using alkaline phosphatase-labeled oligodeoxynucleotide probe. In Methods in Molecular Biology, Protocols in Molecular Neurobiology, (A. Longstaff, and R Revest, eds.), Vol. 13, pp. 167-179. Humana Press, Totowa, New Jersey. 

The RPIA technology has been enhanced in the Stratus CS system by utilization of a dendrimer-antibody complex in which the analyte-specific capture antibody is covalenty coupled onto a dendrimer. The test packs in the Stratus CS system include dendrimer-capture antibody complex reagent, the alkaline phosphatase labeled antibody conjugate reagent, the substrate-wash reagent and a piece of glass fiber filter paper as the solid phase. Preparation and unique properties associated with these dendrimer-coupled antibody complexes are described below. 

An elegant approach is to capture the target DNA or RNA with specific oligonucleotides on to a microwell plate. Synthetic branched DNA bearing multiple alkaline phosphatase-labeled probes hybridizes to the target. A chemiluminescent substrate is added to produce signal. This branched DNA assay has been used in infectious disease detection (W3). 

Detection reagent (substrate) for enzyme-labeled antibody 2,2-azino-di(3-ethyl-benzthiazohne sulfonate-6) (ABTS) 0.3 g/L in 0.15 M sodium citrate with 0.1% H2O2 for the detection of horseradish peroxidase-labeled secondary antibody or p-nitrophenyl phosphate (pNPP) 1 g/L in 1M diethanolamine in water for the detection of an alkaline phosphatase-labeled antibody (Kirkegaard and Perry Laboratories). 

Secondary antibodies are enzyme-linked antibodies directed against the primary antibody host animal s immunoglobulin (usually an IgG). If the primary antibody is mouse anticytokeratin the secondary antibody would be horseradish peroxidase-labeled or alkaline phosphatase-labeled antimouse IgG. 

Nonradioactive in Situ Hybridization Using Alkaline Phosphatase-Labelled Oligonucleotides S. J. Augood, E. M. McGowan, B. R. Finsen,... 

Dual endogenous enzyme block Horseradish peroxidase and alkaline phosphatase labels... 

Levamisole + chromogen except intestinal alkaline phosphatase Alkaline phosphatase label... 

Fig. 1. A schematic representation of the twin-site ELISA for fos and myc proteins. The signal from the alkaline phosphatase label is amplified via the AMPAK enzyme cycle to generate the red formazan dye.

Any detecdon system can be used (e.g., I-labeled or alkaline phosphatase-labeled antirat Ig). We find it convenient to use the galac-tosidase label plus a substrate, 4-methylumbelliferyl -galactoside, which is converted to a highly fluorescent product. However, fluorescence detection is only important for high sensitivity assays as described in Chapter 35. 

In Situ Hybridization to Human Chromosomes of an Alkaline Phosphatase-Labeled Centromeric Probe... 

Figure 2. Coronin 1C in melanoma. A) Immunohistochemical staining of the indicated tissue samples for Coronin 1C. S m sections from melanoma tumors were stained with a new Coronin 1C specific mAb (Roadcap and Bear, unpublished reagent) for 30min at 37°C with a steam heat-induced epitope retrieval, using the streptavidin/biotin method with an alkaline phosphatase label and Permanent Red (Dako) as the chromogen and then stained with hematoxylin. B) qRT-PCR analysis of the indicated melanoma cell lines treated with the Erk inhibitor U0126 or vehicle control for 24 hours.Dotted line indicates lx threshold.

In the enzyme-multiplied immunoassay techniques (EMIT), the antigen or antibody is labeled with an enzyme (e.g., iysozyme, alkaline phosphatase, horseradish peroxidase, or glucose-6-phosphate dehydrogenase) instead of a radioisotope. For example, an alkaline phosphatase-labeled drug can be made to compete with an unlabeled drug for binding sites on... 

An amperometric immunosensor using sequential injection analysis techniques to detect the herbicide 2,4-D in water was described by Wilmer and Trau [102,103]. This rapid competitive EIA used an alkaline phosphatase-labelled monoclonal antibody directed against the herbicide and an immunoreactor with 2,4-D immobilized via BSA, either to Eupergit in a column or directly to the surface of a glass capillary. A detection limit of the immunosensor at 0.1 (jLg 2,4-D 1, without enrichment of the analyte, pointed to the feasibility of making automatic measurements of 2,4-D in drinking and ground water. 

Anti-digoxigenin Fab fragments, alkaline phosphatase labeled, 150 U/mL (Boehringer Mannheim). 

Alkaline phosphatase-labeled goat antimouse IgG (Cappel). 

Incubate spotted membranes for 2 h with 0.025 pg/mL alkaline phosphatase-labeled goat antimouse IgG (Cappel). 

Chemiluminescence assays are ultrasensitive (attomole to zeptomole detection limits) and have wide dynamic ranges. They are now widely used in automated immunoassay and DNA probe assay systems, (e.g., acridinium ester and acri-dinium sulfonamide labels and 1,2-dioxetane substrates for alkaline phosphatase labels and the enhanced-luminol reaction for horseradish peroxidase labels [see Chapter 9]). 

---