Radiolabelling studies

Recently it was shown by radiolabeling studies that the formation of the serrulatane skeleton is catalyzed by the pseudopterosin diterpene cyclase, which can be considered as a key enzyme in terpene biosynthetic pathways (Scheme 2). The elisabethatriene cyclase is a monomer with a molecular mass of47kDa [25]. 

Radiolabeled studies in rats demonstrated highest exposure to radioactivity from an i.v. C-brinzolamide dose in tissues containing high CA concentrations. These included liver, kidneys, spleen, lungs and salivary glands. Radioactivity concentrations in fat, nerve, skeletal muscle, skin, eyes and testes were low. Experiments in pregnant and lactating rats demonstrated transfer of radioactivity across the placental barrier and secretion of low concentrations in milk. 

Figure 173 The hydroxyl group on the phenyl azide ring of SASD may be iodinated with, 2SI to allow radiolabeling studies to be done on photolyzed conjugates.

All the techniques described in this chapter contribute to improved metabolite characterization. Notably, these techniques will enable the generation of extended time profiles for plasma radioactivity, the assessment of free metabolite concentrations following plasma dialysis, and the characterization of metabolites at very low levels of exposure, for example, following inhaled or dermal routes of administration. Furthermore, the use of high-sensitivity techniques could impact the design of radiolabel studies, for example, by enabling a lower radiolabel dose to be administered to human subjects without compromising the ability to characterize the metabolic fate of the compound of interest. 

Stizolobinic acid 15 has been formally proposed as a biosynthetic precursor to acromelic acid A 520 and, importantly, radiolabeling studies have shown that it is derived biosynthetically from L-dopa.21... 

DeBolt, S., Hardie, J., Tyerman, S., and Ford, C.M., 2004, Comparison and synthesis of raphide crystals and druse crystals in berries of Vitis vinifera L. cv. Cabernet Sauvignon Ascorbic acid as precursor for both oxalic and tartaric acids as revealed by radiolabelling studies. Aust. J. Grape Wine Res. 10 134—142. 

Based on a radiolabel study in mice, most of the absorbed butadiene is exhaled as the parent compound, with a lesser amount exhaled as C02- Smaller amounts of butadiene and/or its metabolites are detected in urine and feces, with most of the label being eliminated from the carcass within 65 h. This is... 

Djerassi and co-workers reported the first documentation by radiolabeling studies that cholesterol can be produced in sponges by dealkylation of 24(28)-unsaturated precursors, that the reaction... 

The most likely candidate for the phosphoethanolamine donor is phosphatidylethanol-amine. Metabolic radiolabeling studies demonstrate that [ H]ethanolamine is incorporated into CDP-phosphoethanolamine before it is transferred to phosphatidylethanolamine and attached to the GPI core glycan. CDP-ethanolamine, however, is not a donor since it is not required for, nor does it affect, GPI anchor biosynthesis [62]. Consistent with this observation is the lack of [ HJglucosamine incorporation into GPI anchors in yeast mutants that do not synthesize phosphatidylethanolamine from CDP-ethanolamine yet can construct GPI anchors [88]. Direct evidence for a phosphatidylethanolamine donor is still lacking. 

The identity of the glycosylated polypeptides as precursor forms of the ricin subunits was further confirmed by in vivo radiolabelling studies [136]. 

Radiolabeled studies are the cornerstone of the chemistry requirements because they fulfill two critical functions. These are (i) to determine the metabolites of the drug and (ii) to determine the kinetic behavior of the residue as it depletes following cessation of the drug treatment. 

The understanding of the chemical details of the a-oxoamine synthases mechanism derived from a series of complementary investigations was included radiolabeling studies on ALAS, kinetic studies on and ALAS, and detailed crystallographic studies on KBL and The reaction catalyzed by... 

At the completion of the test the exposed shafts (not used in the radiolabeled studies) were placed in buffered glutaraldehyde. The shafts were post-fixed and critical-point dried (9). The critical-point-dried coatings were removed, embedded in... 

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