Choice of label

The choice of label will depend on the application envisaged. Enzymes are widely applicable they are used in assays, such as ELISAs, and for detection of antigen blotted or dotted on membranes or embedded in tissue sections. Enzyme labels have also be used for the location of antigen in electron microscope sections but gold labelled antibodies (Chapter 11) are now extensively employed for this purpose. Antibodies labelled with a fluorescent molecule are used in assays and for the detection of antigens in tissue sections and also for flow cytometiy and fluorescence-activated cell sorting. 

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The intense Texas Red fluorophore has a QY that is inherently higher than the tetrameth-ylrhodamine or Lissamine rhodamine B derivatives. Texas Red s luminescence is shifted maximally into the red region of the spectrum, and its emission peak only minimally overlaps with that of fluorescein. This makes Texas Red derivatives among the best choices of labels for use in double-staining techniques. 

Ease of separation of tritiated products from a reaction medium is an important feature in the choice of labeling procedure. Sometime ago we used polymer-sup-ported acid and base catalysts [12, 13] to good effect and with the current interest in Green Chemistry one can expect to see more studies where the rate accelerations observed under microwave-enhanced conditions are combined with the use of solid catalysts such as Nafion, or zeolites. 

The choice of label is important and the most common are listed in Table 7.3. 

Labeling with two different dyes typically requires the final RNA construct to be assembled from at least two fragments (Scheme 3.1). Depending on the choice of labeling sites, one of the following assembly strategies can be pursued ... 

Other methods of assembly (1. a—e and 2.a) are easier to implement, but they restrict the choice of labeling sites to the ends of the molecule (l.a—c and 2. a), and/or require assumptions that modifications of the sequence— that is, binding of oligos at the ends and at internal sites (l.b—d), circular permutations (l.e) or nicks in the continuous backbone (2.a)—do not affect the dynamics of interest. Testing such assumptions can be nontrivial. 

The aim of this study was to show wide spectrum of possible labels for proteins and the techniques for incorporating them into protein molecules. The choice of label used and the method of labeling is closely related to the purpose for which the labeled protein is to be employed. Although there are many different approaches, they can often fulfil the same final goal (e.g. various protein labels in immunoanalysis). 

Constraints imposed by the intended application may limit the choice of labeling methods (Table 7.2). For example, when the probe should be intact, such as in Sj mapping, labeling by nick translation should be avoided. In contrast, for most slot blot and in situ hybridizations, nick translation or random primer extension methods provide suitable probes with an optimum label density, often with the added benefit of ss extensions on the duplex offering the possibility of amplification through hyperpolymer formation. 

The target nucleic acid is labeled with a radioisotope or or a fluorescent compound (e. g., CY5) and hybridised to a scanning array. The choice of label depends on the application. For example, when studying folding of a target nucleic acid, it may be more appropriate to label it with a radioisotope rather than CY5 because the bulky CY5 groups may interfere with or alter the folding of the labeled compound. 

The shape of the container, its material and the closure type to be labelled all have a major influence on the choice of labelling machine. Cylindrical containers are the easiest to label, provided that they are clean and parallel sided with no protrusions anywhere on the plane to be labelled. Any other shape increases the difficulty of label placement and wipedown. If the closure of the container is of the dispensing type, e.g. aerosol valve, holding the container by means of top pressure during labelling will actuate the aerosol. 

The subject of phospholipase assays has been concisely reviewed [1-5]. A standard approach employs phospholipids with radioisotopes incorporated into specific positions in the molecule. By the appropriate choice of labeling, the specificity of the enzymes can readily be established and as little as a few picomoles of product can be detected. The use of isotopes has been helpful in the measurement of phospholipase activity using the membranes of whole cells or isolated subcellular fractions previously labeled with radioactive phospholipid precursors. 

We have tried to emphasize not only the importance of the problem of the availability, but also that of the precise specifications of C, S, (etc.) labelled compounds, namely the specificity of the labelling position and the radiochemical purity. These two parameters are of vital importance for the future application of the labelled molecule in medicine, biology and the environmental sciences. Furthermore, two factors must be considered for the reliability of metabolic studies of drugs and pesticides correct choice of labelling position, since a position that is too exposed can result in loss of the label and consequently incomplete results the other factor is that of stable isotopes and the so-called isotopic effect. 

Immunoassays for small organic compounds usually are formatted as competition assays (13.141. There are many assay formats and choices of label for the eventual quantification of binding. An equilibrium is approached for formatirxi of complexes between the antibody, labeled or immobilized hapten (hapten ), and fiee analyte in the sample, according to the following equation. 

The choice of labeled nucleotide can be influenced by a number of experimental factors these are discussed in Section II,D. Note that modified dUTPs (e.g., FlTC-dUTP, digoxigenin-dUTP) are dTTP analogs. 

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