Or 14C-labelled

Table 1 Details of polymerisations killed with tritiated water or 14C-labelled 2-propanol...

A further study by Olken and collaborators112 describes inactivation of mouse iNOS by /Vc -rncl.hyI-1.-arginine. The inactivation occurs only in the presence of oxygen. Only a small amount of 3H or 14C label from the labeled methyl group of AG-methyl-L-arginine... 

The problem of radiochemical purity with respect to the chemical state of aged tritium or 14C-labeled compounds is still more acute. Because of the short range... 

Recent drug assay development involved LC-MS methods (Caubet et al. 2004 Kanazawa et al. 2000). A less practical breath test, using 13C or 14C labeled caffeine, can also be used (Kalow and Tang 1991). 

In vitro and ex vivo studies have shown that FATPs transport LCFAs and very long-chain fatty acids (VLCFAs) but no medium-chain fatty acids, fatty acid esters, or lipid-soluble vitamins [4]. LCFA transport is inhibited by prior protease treatment. Synthetic substrates for FATPs include 14C-labeled fatty acids and the fluorescently labeled fatty acid analogue C1 -BODEP Y-Cl 2. Using the latter substrate, differences in fatty acid uptake kinetics between FATP expressing 3T3 LI adipocytes and 3T3 LI fibroblasts, which are devoid of FATPs, can be readily appreciated (Fig. 2). 

Experiments with 14C-labelled substrates also demonstrated conclusively the intramolecularity of the rearrangement. The generally accepted scheme involves the formation of the dienone LXXXV which can lose a hydrogen atom if R = H, to form the ortho product or if R H further rearrangement to LXXXVI occurs with subsequent formation of the para product, viz. 

The inhibition of Streptococcus mutans adherence to hydroxyapatite with combinations of alkyl phosphates and nonionic surfactants was tested. Seven alkyl phosphate derivatives and three nonionic surfactants were examined for their ability to inhibit the adherence of 3H-labeled cells of S. mutans to hydroxyapatite treated with buffer or parotid saliva. No compound by itself effectively hindered binding of bacteria to hydroxyapatite. A combination of certain of the alkyl phosphates, notably a disodium phosphate of 1-octadecanol, and nonionic surfactant at a 1 1 molar ratio gave a strong inhibition of S. mutans adherence. Treatment with this combination resulted in 98% reduction of adherence. Adsorption of the two types of surface-active agents alone and in combinations was studied using 14C-labeled agents. Electrophoretic measure-... 

Albemarle) has shown unique resistance to extraction from polyolefins. No radioactivity was detected in water run through a MDPE pipe stabilised with 14C-labelled Ethanox 330 for 10 months at ambient conditions, or in an accelerated 3-month test at 80 °C (limit of detection 25ppb). 

The incorporation of 14C into compounds at a suitable site often requires extensive and complicated syntheses, and thus a relatively long time. This usually means that 14C-labeled compounds are unsuitable for studies to be carried out during discovery. There are however, very rapid methods for incorporating 3 H into compounds. The newer methods, generally involving metal-catalyzed exchange reactions [15-18], in our experience, mean that suitable labels can often be prepared in 2 or 3 weeks. These time scales make the approach viable for discovery support. Additionally, and importantly, these methods can lead to specific incorporation of tritium. 

Direct Methods. The classical approach has been to prepare tritiated or carbon labeled analogs of the parent hydrocarbons which may then be used in animal or in vitro experiments. Tritiated compounds are generally easier to prepare, using exchange reactions on the parent hydrocarbon, than their 14C analogs and have higher specific activities. However, during the metabolism of such compounds, some of the tritium is released as tritiated water, either directly or... 

These factors make 125I the iodine label of choice for radiolabeling biological molecules. Its commercial availability from a number of suppliers at relatively low cost further adds to its popularity. Even though it has lower specific activity than 131I, iodine-125 still provides much greater sensitivity than 14C, 32P, 35S, or 3H in labeling biomolecules. In fact, the use of a radioactive iodine label can create probes that have 150-fold more sensitivity than tritiated molecules and as much as 35,000 times the detectability of 14C-labeled molecules (Bolton and Hunter, 1986). 

The standard work of Evans [2] as well as a survey of the papers produced in the Journal of Labeled Compounds and Radiopharmaceuticals over the last 20 years shows that the main tritiation routes are as given in Tab. 13.1. One can immediately see that unlike most 14C-labeling routes they consist of one step and frequently involve a catalyst, which can be either homogeneous or heterogeneous. One should therefore be able to exploit the tremendous developments that have been made in catalysis in recent years to benefit tritiation procedures. Chirally catalyzed hydrogenation reactions (Knowles and Noyori were recently awarded the Nobel prize for chemistry for their work in this area, sharing it with Sharpless for his work on the equivalent oxidation reactions) immediately come to mind. Already optically active compounds such as tritiated 1-alanine, 1-tyrosine, 1-dopa, etc. have been prepared in this way. 

Another method is based on the same principle,112 in which the [14C]labelled methyl ester of D-galacturonan is prepared by esterification of pectic acid with [,4C]diazomethane. In the course of the enzymic de-esterification, aliquots are removed, and the unreacted substrate is precipitated with acidified ethanol or 1-propanol. After centrifugation, the labelled methanol in the supernatant liquor is determined in a liquid scintillation counter. An advantage of this method lies in the possibility of using, as substrates, short-chain oligo-D-galactosiduronates partially esterified with [14C]methanol. These substrates, beginning with the trisaccharide, are not soluble in 1 4 80% phenol-diethyl ether, which is used for the extraction of enzymically released, labelled methanol. 

Oral exposure to single dose of 50, 100, or 150 mg/kg of 14C-labeled toxaphene... 

Genetic analysis indicates that two of the 10 sad mutants of A. strigosa that we isolated represent different mutant alleles at the Sadi locus.6 These mutants accumulate radiolabelled 2,3-oxidosqualene but not p-amyrin when the roots are fed with 14C-labelled precursor mevalonic acid, suggesting that the triterpenoid pathway is blocked between 2,3-oxidosqualene and P-amyrin.34 The roots of these mutants also lack detectable P-amyrin synthase activity, but, like the wild type and the other mutants, are unimpaired in cycloartenol synthase (CS) activity and sterol biosynthesis.34 The transcript levels for AsbASl are substantially reduced in roots of sadl mutants, while AsCSl transcript levels are unaffected,35 suggesting that the sadl mutants are either mutated in the AsbASl gene itself or in a gene involved in its regulation. 

Recently an isotope dilution method has been reported O for assaying neomycin sulphate. However, it is first necessary to prepare 14C-labelled neomycin sulphate. This is accomplished by adding l4C-labelled glucose to a small-scale fermentation of 5. nad-iat. l4C-labelled neomycin can then be extracted by solvent-extraction or by ion-exchange chromatography. 

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