Immunological molecules, detection

Probe Single-stranded DNA or RNA molecules of specific base sequence, labeled either radioactively or immunologically, that are used to detect the complementary base sequence by hybridization. 

Among the many immunological assay methods, the enzyme-linked immunosorbent assay methods (ELISA) are the most popular methods. ELISA can detect both antigen molecules and antibody molecules with only a slight modification of the procedure. The direct-binding and sandwich methods that are used for the... 

Lectins, or proteins with specific binding sites for carbohydrates, can be used as targeting molecules to localize particular glycoconjugates such as glycoproteins or glycolipids on cell surfaces (Fig. 373). Labeled with gold particles, lectins are important probes for detection of cell surface components and intracellular receptors and in immunological or biochemical assay procedures (Bog-Hansen et al., 1978 Kimura et al., 1979 Nicolson, 1978 Roth, 1983 Benhamou et al., 1988 Nakajima et al., 1988). 

Harn, D.A., Mitsuyama, M., Huguenel, E.D. and David, J.R. (1985) Schistosoma mansoni detection by monoclonal antibody of a 22,000-dalton surface membrane antigen, which may be blocked by host molecules on lung stage parasites. The Journal of Immunology 135, 21 15-2120. 

One further problem is the large overshoot in ABA production in wilted leaves. With applied ABA a doubling of the ABA content of the leaf is usually adequate for stomatal closure, while increases up to 40-fold have been reported in wilted leaves. However, extractions of whole leaves do not take into account the location of ABA within the leaf. Perhaps much of the hormone is sequestered in a compartment that has no access to the guard cells. Thus, it would be of much importance to determine the distribution of ABA at the tissue level as well as its intracellular location. Since ABA is a small water-soluble molecule, conventional fractionation techniques may not be suitable to determine its distribution in various organelles. A highly specific immunological method for detection of ABA has recently been developed (38, 39). It is conceivable that this technique could be further developed for determining the cellular localization of ABA as has already been done for the photoreceptor phytochrome (77, 78). 

Because a library can contain thousands of different clones, it can be difficult to isolate a clone with DNA of specific interest. This is because the majority of cloned DNAs do not contain a readily selectable genetic marker, such as antibiotic resistance, or lead (as discussed earlier) to the production of a foreign protein. Methods to achieve this have been developed and utilize hybridization, immunochemical, and structural techniques. A specific DNA sequence of only several kilobases can be isolated from a genome containing in excess of 106 kilobases. Hybridization requires a radioactive DNA or RNA molecule (a probe) that is complementary (or partially so) to the sequence of the cloned DNA. Immunologic techniques require that the polypeptides coded by the DNAs of interest are available and have specific antigenic properties that allow detection. Structural analysis can also be used when the other techniques are inapplicable. 

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