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  • 1
    Digitale Medien
    Digitale Medien
    NifL of Klebsiella pneumoniae carries an N-terminally bound FAD cofactor, which is not directly required for the inhibitory function of NifL (1997)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 157 (1997), S. 0 
    Details
    ISSN: 1574-6968
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: In Klebsiella pneumoniae NifL antagonizes the action of the transcriptional activator NifA in the presence of molecular oxygen or combined nitrogen. To determine what cofactors might be involved in the oxygen sensing mechanism, we purified and analyzed fusion proteins made between the Escherichia coli maltose binding protein, MalE, and NifL. NifL synthesized and purified under strictly anaerobic conditions did not contain significant amounts of iron or acid-labile sulfur indicating the absence of an oxygen sensing iron-sulfur cluster. However, NifL protein purified in its inhibitory form contained 0.3±0.01 mol FAD and less than 0.01 mol FMN per mol NifL suggesting the presence of FAD as a cofactor. Characterization of NifL synthesized in the absence of oxygen and combined nitrogen showed that the non-inhibitory form of NifL also contained FAD (0.54 mol FAD per mol NifL). Using fusions between MalE and different portions of NifL we localized the binding site of FAD to the N-terminal domain of NifL. These results and our previous observation that the C-terminal domain of NifL is sufficient to inhibit NifA activity indicate that the N-terminally bound FAD is not directly required for the inhibitory activity of NifL. This observation is supported by the finding that purified apoprotein of NifL was still able to inhibit transcriptional activation by NifA in vitro.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1574-6968.1997.tb12791.x
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  • 2
    Digitale Medien
    Digitale Medien
    Unique mechanistic features of post-translational regulation of glutamine synthetase activity in Methanosarcina mazei strain Gö1 in response to nitrogen availability (2005)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 55 (2005), S. 0 
    Details
    ISSN: 1365-2958
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Medizin
    Notizen: PII-like signal transduction proteins are found in all three domains of life and have been shown to play key roles in the control of bacterial nitrogen assimilation. This communication reports the first target protein of an archaeal PII-like protein, representing a novel PII receptor. The GlnK1 protein of the methanogenic archaeon Methanosarcina mazei strain Gö1 interacts and forms stable complexes with glutamine synthetase (GlnA1). Complex formation with GlnK1 in the absence of metabolites inhibits the activity of GlnA1. On the other hand, the activity of this enzyme is directly stimulated by the effector molecule 2-oxoglutarate. Moreover, 2-oxoglutarate antagonized the inhibitory effects of GlnK1 on GlnA1 activity but did not prevent GlnK1/GlnA1 complex formation. On the basis of these findings, we hypothesize that besides the dominant effector molecule 2-oxoglutarate, the nitrogen sensor GlnK1 allows finetuning control of the glutamine synthetase activity under changing nitrogen availabilities and propose the following model. (i) Under nitrogen limitation, increasing concentrations of 2-oxoglutarate stimulate maximal GlnA1 activity and transform GlnA1 into an activated conformation, which prevents inhibition by GlnK1. (ii) Upon a shift to nitrogen sufficiency after a period of nitrogen limitation, GlnA1 activity is reduced by decreasing internal 2-oxoglutarate concentrations through diminished direct activation and by GlnK1 inhibition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2958.2005.04511.x
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  • 3
    Digitale Medien
    Digitale Medien
    Tungstate can substitute for molybdate in sustaining growth of Methanobacterium thermoautotrophicum (1994)
    Springer
    Archives of microbiology 161 (1994), S. 220-228 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Formylmethanofuran dehydrogenase ; Tungsten enzymes ; Molybdopterin dinucleotides ; Methanogenesis ; Archaea ; Archaebacteria ; Methanobacterium thermoautotrophicum ; Methanobacterium wolfei
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Methanobacterium thermoautotrophicum (strain Marburg) was found to grow on media supplemented with tungstate rather than with molybdate. The Archaeon then synthesized a tungsten iron-sulfur isoenzyme of formylmethanofuran dehydrogenase. The isoenzyme was purified to apparent homogeneity and shown to be composed of four different subunits of apparent molecular masses 65 kDa, 53 kDa, 31 kDa, and 15 kDa and to contain per mol 0.4 mol tungsten, 〈0.05 mol molybdenum, 8 mol non-heme iron, 8 mol acid-labile sulfur and molybdopterin guanine dinucleotide. Its molecular and catalytic properties were significantly different from those of the molybdenum isoenzyme characterized previously. The two isoenzymes also differed in their metal specificity: the active molybdenum isoenzyme was only synthesized when molybdenum was available during growth whereas the active tungsten isoenzyme was also generated during growth of the cells on molybdate medium. Under the latter conditions the tungsten isoenzyme was synthesized containing molybdenum rather than tungsten.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00248696
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  • 4
    Digitale Medien
    Digitale Medien
    Tungstate does not support synthesis of active formylmethanofuran dehydrogenase in Methanosarcina barkeri (1994)
    Springer
    Archives of microbiology 161 (1994), S. 528-530 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Tungsten enzymes ; Molybdenum enzymes ; Formylmethanofuran dehydrogenase ; Methanogenic Archaea ; Methanosarcina barkeri ; Methanobacterium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Cell extracts of Methanosarcina barkeri grown on methanol in media supplemented with molybdate exhibited a specific activity of formylmethanofuran dehydrogenase of approximately 1 U (1 μmol/min)/mg protein. When the growth medium was supplemented with tungstate rather than with molybdate, the specific activity was only 0.04 U/mg. Despite this reduction in specific activity growth on methanol was not inhibited. An inhibition of both growth and synthesis of active formylmethanofuran dehydrogenase was observed, however, when H2 and CO2 were the energy substrates. The results indicate that, in contrast to Methanobacterium wolfei and Methanobacterium thermoautotrophicum, M. barkeri possesses only a molybdenum containing formylmethanofuran dehydrogenase and not in addition a tungsten isoenzyme.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00307775
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  • 5
    Digitale Medien
    Digitale Medien
    Tungstate can substitute for molybdate in sustaining growth of Methanobacterium thermoautotrophicum (1994)
    Springer
    Archives of microbiology 161 (1994), S. 220-228 
    Details
    ISSN: 1432-072X
    Schlagwort(e): Key words: Formylmethanofuran dehydrogenase – Tungsten enzymes – Molybdopterin dinucleotides – Methanogenesis – Archaea – Archaebacteria –Methanobacterium thermoautotrophicum–Methanobacterium wolfei
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Methanobacterium thermoautotrophicum (strain Marburg) was found to grow on media supplemented with tungstate rather than with molybdate. The Archaeon then synthesized a tungsten iron-sulfur isoenzyme of formylmethanofuran dehydrogenase. The isoenzyme was purified to apparent homogeneity and shown to be composed of four different subunits of apparent molecular masses 65 kDa, 53 kDa, 31 kDa, and 15 kDa and to contain per mol 0.4 mol tungsten, 〈0.05 mol molybdenum, 8 mol non-heme iron, 8 mol acid-labile sulfur and molybdopterin guanine dinucleotide. Its molecular and catalytic properties were significantly different from those of the molybdenum isoenzyme characterized previously. The two isoenzymes also differed in their metal specificity: the active molybdenum isoenzyme was only synthesized when molybdenum was available during growth whereas the active tungsten isoenzyme was also generated during growth of the cells on molybdate medium. Under the latter conditions the tungsten isoenzyme was synthesized containing molybdenum rather than tungsten.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00248696
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  • 6
    Digitale Medien
    Digitale Medien
    Internal Glutamine and Glutamate Pools in Klebsiella pneumoniae Grown Under Different Conditions of Nitrogen Availability (2000)
    Springer
    Current microbiology 41 (2000), S. 357-362 
    Details
    ISSN: 1432-0991
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Internal pool sizes of glutamine and glutamate in Klebsiella pneumoniae grown under nitrogen limitation or nitrogen sufficiency were measured to study the signal transduction of external nitrogen limitation. K. pneumoniae cells were grown in an anaerobic, ammonium-limited chemostat culture. At a growth rate of 0.217 h−1, the steady state ammonium concentration in the culture was 55 μm, correlating with repression of the nitrogen fixation (nif) genes. At growth rates below 0.138 h−1, the ammonium concentration in the culture dropped below 0.5 μm and the nif genes became derepressed. During the transition from nitrogen sufficiency to nitrogen limitation, the internal glutamine pool in K. pneumoniae decreased by a factor of approximately 6. The glutamate pool, however, remained stable. Similarly, in anaerobic batch cultures with different limiting nitrogen sources, the glutamine pool generally decreased by a factor of 7 to 9 when nif gene derepression was achieved. All the limiting nitrogen sources used resulted in decreased growth rates compared with growth under nitrogen excess, suggesting an inverse relationship between glutamine pool size and doubling time. These studies indicate that K. pneumoniae perceives external nitrogen limitation as internal glutamine limitation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s002840010149
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  • 7
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    Water column biogeochemistry of oxygen minimum zones in the eastern tropical North Atlantic and eastern tropical South Pacific oceans (2016)
    In:  EPIC3Biogeosciences, 13(12), pp. 3585-3606, ISSN: 1726-4189
    Details
    Publikationsdatum: 2017-06-15
    Beschreibung: Recent modeling results suggest that oceanic oxygen levels will decrease significantly over the next decades to centuries in response to climate change and altered ocean circulation. Hence, the future ocean may experience major shifts in nutrient cycling triggered by the expansion and intensification of tropical oxygen minimum zones (OMZs), which are connected to the most productive upwelling systems in the ocean. There are numerous feedbacks among oxygen concentrations, nutrient cycling and biological productivity; however, existing knowledge is insufficient to understand physical, chemical and biological interactions in order to adequately assess past and potential future changes. In the following, we summarize one decade of research performed in the framework of the Collaborative Research Center 754 (SFB754) focusing on climate–biogeochemistry interactions in tropical OMZs. We investigated the influence of low environmental oxygen conditions on biogeochemical cycles, organic matter formation and remineralization, greenhouse gas production and the ecology in OMZ regions of the eastern tropical South Pacific compared to the weaker OMZ of the eastern tropical North Atlantic. Based on our findings, a coupling of primary production and organic matter export via the nitrogen cycle is proposed, which may, however, be impacted by several additional factors, e.g., micronutrients, particles acting as microniches, vertical and horizontal transport of organic material and the role of zooplankton and viruses therein.
    Repository-Name: EPIC Alfred Wegener Institut
    Materialart: Article , peerRev
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