Chemical labeling radioactive labels

Forster, A.C., Mclnnes, J.L., Skingle, D.C., and Symons, R.H. (1985) Non-radioactive hybridization probes prepared by the chemical labeling of DNA and RNA with a novel reagent, photobiotin. Nucleic Acid Res. 13, 745-761. 

The field of application for the isotope dilution method with radioactive tags, extends to measurements using stable isotope. Mass spectrometry or nuclear magnetic resonance are used to determine the variations in the isotopic concentrations. Chemical labelling using externally introduced tags consists of the addition to a sample of the same analyte but containing a stable isotope (e.g. H, C, N) as an internal standard. This method is as much used for molecular species as for atoms (around 60 have stable isotopes). 

The shortcomings of cellulose itself, and of cellulose derivatives as substrates for studying the mechanism of cellulase action are pointed out. The oligosacchardies—prepared with a radioactive, or chemical label—are useful in determining the bond preference of enzymes and hence whether a component is of the endo-p-1 — 4 glucanase or exo-p-1 — 4 glucanase type. 

Some further details are the following. Film nonideality may be allowed for [192]. There may be a chemical activation barrier to the transfer step from monolayer to subsurface solution and hence also for monolayer formation by adsorption from solution [294-296]. Dissolving rates may be determined with the use of the radioactive labeling technique of Section III-6A, although precautions are necessary [297]. 

Radiochemical tracers, compounds labeled with radioisotopes (qv), have become one of the most powerful tools for detection and analysis in research, and to a limited extent in clinical diagnosis (see Medical IMAGING TECHNOLOGY). A molecule or chemical is labeled using a radioisotope either by substituting a radioactive atom for a corresponding stable atom in the compound, such as substituting for H, for or for P, and for for... 

Synthetic chemical approaches to the preparation of carbon-14 labeled materials iavolve a number of basic building blocks prepared from barium [ CJ-carbonate (2). These are carbon [ C]-dioxide [ CJ-acetjlene [U— C]-ben2ene, where U = uniformly labeled [1- and 2- C]-sodium acetate, [ C]-methyl iodide, [ C]-methanol, sodium [ C]-cyanide, and [ CJ-urea. Many compHcated radiotracers are synthesized from these materials. Some examples are [l- C]-8,ll,14-eicosatrienoic acid [3435-80-1] inoxn. [ CJ-carbon dioxide, [ting-U— C]-phenyhsothiocyanate [77590-93-3] ftom [ " CJ-acetjlene, [7- " C]-norepinephrine [18155-53-8] from [l- " C]-acetic acid, [4- " C]-cholesterol [1976-77-8] from [ " CJ-methyl iodide, [l- " C]-glucose [4005-41-8] from sodium [ " C]-cyanide, and [2- " C]-uracil [626-07-3] [27017-27-2] from [ " C]-urea. All syntheses of the basic radioactive building blocks have been described (4). 

Radioactive tracers account for about 20% of the worldwide market for consumables and reagents for life science research. In 1994 the value was estimated at about 300 million. The principal fuU line manufacturers are Du Pont—NEN Research Products (Boston, Massachusetts) and Amersham International (Amersham, U.K.). These companies share roughly equaHy about 85% of the radiochemicals worldwide market. In addition to an extensive line of catalog products, these suppHers offer custom labeling and custom synthesis services. The rest of the market is shared by producers of a limited range of products or services, such as ICN Biomedicals (Costa Mesa, California) and American Radiolabeled Chemicals (St. Louis, Missouri). 

Eor virtually all radiopharmaceuticals, the primary safety consideration is that of radiation dosimetry. Chemical toxicity, although it must be considered, generally is a function of the nonradio active components of the injectate. These are often unreacted precursors of the intended radioactive product, present in excess to faciUtate the final labeling reaction, or intended product labeled with the daughter of the original radioactive label. 

The base-specific chemical cleavage (or Maxam-Gilbert) method starts with a single-stranded DNA that is labeled at one end with radioactive (Double-stranded DNA can be used if only one strand is labeled at only one of its ends.) The DNA strand is then randomly cleaved by reactions that specifically fragment its sugar-phosphate backbone only where certain bases have been chemically removed. There is no unique reaction for each of the four bases. However,... 

Another widely used approach to the elucidation of metabolic sequences is to feed cells a substrate or metabolic intermediate labeled with a particular isotopic form of an element that can be traced. Two sorts of isotopes are useful in this regard radioactive isotopes, such as and stable heavy isotopes, such as or (Table 18.3). Because the chemical behavior of isotopically labeled compounds is rarely distinguishable from that of their unlabeled counterparts, isotopes provide reliable tags for observing metabolic changes. The metabolic fate of a radioactively labeled substance can be traced by determining the presence and position of the radioactive atoms in intermediates derived from the labeled compound (Figure 18.13). 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

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