Isotope Uptake

Douka, C.E. and A.C. Xenoulis. 1991. Radioactive isotope uptake in a grass-legume association. Environ. Pollut. 73 11-23. 

Applications of isotopes in biochemistry have been manifold. Besides tracing pathways and following the rates of isotope uptake and their intracellular localization, labeling molecules in selected stable positions allowed studies to be made of reaction details, such as those in citrate... 

Attempts to use isolated nuclei for DNA or RNA synthesis were disappointing. Careful study of isotope uptake into RNA showed that, at best, ribonucleotides were only incorporated into transcripts which had already been initiated in vivo. It is only since the 1970s, after... 

Azathioprine allergy can be associated with biochemical hepatitis and a normal liver biopsy, apart form marked lipofuscin deposition (30). These findings, combined with patchy isotope uptake on technetium scintigraphy, are suggestive of focal hepatocellular necrosis. 

Imaging techniques play an important role in the investigation of liver disease. The arrow highlights an area of defective isotope uptake indicating the presence of a liver metastasis in a patient with disseminated malignant di.sea.se. 

Thyroid Uptake Systems. Studies involving absolute thyroid uptake can be performed without imaging using small amounts of or and a simple scintillation probe. This is caUbrated using a phantom, ie, a model of a portion of the human body, loaded with the isotope being used. This instmment is also useful for assaying thyroid exposure to radioiodine among personnel. 

The selective uptake of iodide ion by the thyroid gland is the basis of radioiodine treatment in hyperthyroidism, mainly with although various other radioactive isotopes ate also used (40,41). With a half-life of eight days, the decay of this isotope produces high energy P-particles which cause selective destmction within a 2 mm sphere of their origin. The y-rays also emitted are not absorbed by the thyroid tissue and are employed for external scanning. 

A solution of 4,4-dimethyl-5a-androst-l-en-3-one (128, 14 mg) in cyclohexane (3 ml) is stirred in a microhydrogenation apparatus in the presence of 10 % palladium-on-charcoal (15 mg) at atmospheric pressure and room temperature. The uptake of one eq of deuterium (1.15 ml) is complete in about 1 min and no more deuterium is consumed. After 5 min the catalyst is removed by filtration, and the solvent evaporated under reduced pressure. The resulting l<, 2< -d2-4,4-dimethyl-5a-androstan-3-one (129, 13 mg, 93%), mp 120-122°, exhibits 87% isotopic purity and 13% d species. ... 

The rhodium catalyst (46 mg) is dissolved in acetone (10 ml) in a microhydrogenation apparatus which is then flushed three times with deuterium gas. After stirring the solution in an atmosphere of deuterium for about 1 hr the deuterium uptake ceases and constant pressure is attained. 5a-Cholest-2-ene (136, 19.5 mg) is added and the stirring continued until deuterium uptake ceases (about 3/4 hr). The solvent is evaporated to dryness and the residue is extracted with hexane and the resulting solution filtered through a small alumina column (3 g, activity 111). Evaporation of the hexane gives 2, 3 -d2-5oc-cholestane (137) 18 mg, 92% mp 78-79° isotope composition 94%d2,5%d, andl%do. ... 

Mariotti, A., Mariotti, F., Champigny, M.L., Amarger, N. and Moyse, A. 1982 Nitrogen isotope fractionation associated with nitrate reductase activity and uptake of NO3by pearl millet. Plant Physiology 69 880-884. 

Although the radioactive isotope H has been extensively used for studies on the uptake of xenobiotics into whole cells, the intrusion of exchange reactions and the large isotope effect renders this isotope rather less straightforward for metabolic studies. Both deuterium H-labeled substrates, and oxygen and OH2 have, however, been extensively used in metabolic studies, since essentially pure labeled compounds are readily available and mass spectrometer facilities have become an essential part of structural determination. 

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