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  • 1
    Electronic Resource
    Electronic Resource
    Oxygen radical induced fluorescence in proteins; identification of the fluorescent tryptophan metabolite, N-formyl kynurenine, as a biological index of radical damage (1992)
    Springer
    Amino acids 3 (1992), S. 183-194 
    Details
    ISSN: 1438-2199
    Keywords: Amino Acids ; Protein fluorescence ; Kynurenines ; Oxygen free radicals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of oxygen derived free radicals (OFR) on aromatic and sulphur containing amino acids has been investigated, both in their free form and within protein backbones. Aerated amino acids and proteins in solution were exposed to three discrete OFR generating systems; (1) gamma radiation in the presence or absence of formate (2) photolysis by UV light at 254 and 366 nm, and (3) site specific modification by H2O2 in the presence of CuII ions. A sensitive reverse-phase HPLC technique with dual detection systems (UV absorbance and fluorescence monitoring) was developed to analyse the products of amino acid oxidation. OFR denatured amino acids were chromatographed by this procedure, and all radical species generated, with the exception of the superoxide anion, resulted in the formation of identifiable fluorescent metabolites of tryptophan, kynurenines. The identity of peaks was confimed by spiking with authentic material and scanning absorption spectroscopy. After complete proteolytic hydrolysis, OFR treated proteins were also analysed by this technique; again the dose dependent production of kynurenines was detected in IgG,γ lens crystallins and albumin. Bityrosine was not detected in any of the proteins studied using this procedure, however, several novel unidentified fluorophores were detected in proteolytic hydrolysates, possibly the product of two different amino acid radicals. Immunoglobulin G isolated from the sera of normals and rheumatoid arthritis (RA) patients was examined for the presence of one specific tryptophan metabolite, N-formyl kynurenine. Significantly elevated levels of this metabolite were detected in rheumatoid sera, suggesting increased OFR activity in RA. These results have demonstrated firstly, that specific oxidised products of amino acids are retained in the protein backbone after exposure to OFR generating systems. Secondly, in aerated solution, oxidised tryptophan residues confer the major new visible fluorescence in non-haem proteins, not tyrosine products. In addition, this work has demonstrated that the measurement of a specific product of an oxidised amino acid can be applied to biological macromolecules, and may be important in implicating free radical reactions in certain disease processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00806783
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Determinants of isotopic coupling of CO2 and water vapour within a Quercus petraea forest canopy (1999)
    Springer
    Oecologia 119 (1999), S. 109-119 
    Details
    ISSN: 1432-1939
    Keywords: Key words Stable isotopes ; Carbon ; CO2 ; Water vapour ; Forest canopies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Concentration and isotopic composition (δ13C and δ18O) of ambient CO2 and water vapour were determined within a Quercus petraea canopy, Northumberland, UK. From continuous measurements made across a 36-h period from three heights within the forest canopy, we generated mixing lines (Keeling plots) for δa 13CO2, δa C18O16O and δa H2 18O, to derive the isotopic composition of the signal being released from forest to atmosphere. These were compared directly with measurements of different respective pools within the forest system, i.e. δ13C of organic matter input for δa 13CO2, δ18O of exchangeable water for δa C18O16O and transpired water vapour for δa H2 18O. [CO2] and δa 13CO2 showed strong coupling, where the released CO2 was, on average, 4 per mil enriched compared to the organic matter of plant material in the system, suggesting either fractionation of organic material before eventual release as soil-respired CO2, or temporal differences in ecosystem discrimination. δa C18O16O was less well coupled to [CO2], probably due to the heterogeneity and transient nature of water pools (soil, leaf and moss) within the forest. Similarly, δa H2 18O was less coupled to [H2O], again reflecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The δ18O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO2 and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050766
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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