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  • 1
    ISSN: 1432-0517
    Keywords: Key words Trace elements ; Water ; Intercomparison ; Comparability ; Traceability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract  The sixth round of the International Measurement Evaluation Programme (IMEP) is presented. The programme offers reference values, established by primary methods of measurement, against which participating laboratories can evaluate their performance. The degree of comparability is thus established against the most objective references available at present. In IMEP-6, reference values for total concentrations of 14 trace elements in a synthetic and a natural water were established mainly by isotope dilution mass spectrometry (IDMS). For the majority of the measurands, results traceable to the international system of units (SI) and having expanded uncertainties, U (k=2), of 2% could be established. Measurements results from 165 field laboratories in 29 countries are evaluated and presented as descriptive (regional, national and intercontinental) pictures of the participants' self-declared degree of experience, status of accreditation, performance (including target values for uncertainty set by authorities) and instrumental methods used. The participants' use of certified reference materials and calibrants has been documented, and some comments on this matter are raised. The results and characteristics for IMEP-6 are compared with those of IMEP-3 (1991–1993) and discussed in view of the forthcoming IMEP-9 (1998).
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 1996-07-05
    Description: When the Mg2+ ion in the catalytic center of Escherichia coli RNA polymerase (RNAP) is replaced with Fe2+, hydroxyl radicals are generated. In the promoter complex, such radicals cleave template DNA near the transcription start site, whereas the beta' subunit is cleaved at a conserved motif NADFDGD (Asn-Ala-Asp-Phe-Asp-Gly-Asp). Substitution of the three aspartate residues with alanine creates a dominant lethal mutation. The mutant RNAP is catalytically inactive but can bind promoters and form an open complex. The mutant fails to support Fe2+-induced cleavage of DNA or protein. Thus, the NAD-FDGD motif is involved in chelation of the active center Mg2+.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zaychikov, E -- Martin, E -- Denissova, L -- Kozlov, M -- Markovtsov, V -- Kashlev, M -- Heumann, H -- Nikiforov, V -- Goldfarb, A -- Mustaev, A -- New York, N.Y. -- Science. 1996 Jul 5;273(5271):107-9.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Limnological Institute, Russian Academy of Sciences, Irkutsk, Russia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="" target="_blank"〉PubMed〈/a〉
    Keywords: Amino Acid Sequence ; Aspartic Acid/metabolism ; Binding Sites ; DNA/metabolism ; DNA-Directed RNA Polymerases/*chemistry/genetics/*metabolism ; Dithiothreitol/pharmacology ; Electrophoresis, Polyacrylamide Gel ; Escherichia coli/*enzymology ; Ferrous Compounds/metabolism ; Hydroxyl Radical ; Magnesium/metabolism ; Molecular Sequence Data ; Mutagenesis ; Promoter Regions, Genetic
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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