Isotopes, stable toxicity

Membrane-integrated proteins were always hard to express in cell-based systems in sufficient quantity for structural analysis. In cell-free systems, they can be produced on a milligrams per milliliter scale, which, combined with labeling with stable isotopes, is also very amenable forNMR spectroscopy [157-161]. Possible applications of in vitro expression systems also include incorporation of selenomethionine (Se-Met) into proteins for multiwavelength anomalous diffraction phasing of protein crystal structures [162], Se-Met-containing proteins are usually toxic for cellular systems [163]. Consequently, rational design of more efficient biocatalysts is facilitated by quick access to structural information about the enzyme. 

SAFETY PROFILE Suspected carcinogen. Severe radiotoxicity. Very dangerous to handle. Radiation Hazard Namral isotope 2ioPo (radium-F, uranium series), To.s = 138 days. Decays to stable by alphas of 5.3 MeV. When heated to decomposition it emits toxic and radioactive fumes of Po. See also PLUTONIUM. 

The stable isotope technique described above was used to compare nicotine kinetics in smokers and nonsmokers (Benowitz and Jacob 1993). Labeled (S)-(-)-nicotine was infused intravenously for 30 minutes, and blood and urine samples were collected for 96 hours. Smokers and nonsmokers received the same low dose of nicotine (0.5 micrograms per kilogram per minute (g/kg/min)), and on another day the smokers also received a higher dose of nicotine (2.0 g/kg/min) that resulted in plasma nicotine concentrations similar to those they achieve with smoking. Nonsmokers are unable to tolerate this dose due to toxicity. 

Nicholls et al. have used NMR spectroscopy of urine combined with labelling with stable isotopes such as and to monitor the silent process of deacetylation and subsequent reacetylation (futile deactylation) in the rat as this has implications for the toxicity of paracetamoP and phenacetin. Hull et al. have monitored the metabolites of 5-fluorouracil in plasma and urine using NMR spectroscopy in patients receiving chemotherapy. Akira et al. have used H NMR to study the pharmacokinetics of benzoic... 

Mutlib, A.E., Application of stable isotope-labeled compounds in metabolism and in metabolism-mediated toxicity studies, Chem. Res. Toxicol., 21(9), 1672, 2008. 

Yan and his colleagues used a stable isotope labeled proteome internal standard to analyse protein expression alterations during oxidative stress in breast epithelial cells. Affinity chromatography was combined with MS/MS in the proteomic analysis of human 06-methylguanine-DNA methyltransferase. These studies demonstrated that proteomics can elucidate protein expre-ssions associated with the pharmacological and toxic effects of an anticancer drug when integrated with other biochemical methods. 

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