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  • 1
    Electronic Resource
    Electronic Resource
    The copper site in nitrous oxide reductase (1990)
    Springer
    BioMetals 3 (1990), S. 103-109 
    Details
    ISSN: 1572-8773
    Keywords: Nitrous oxide reductase ; Cytochrome c oxidase ; Cu-Cu interaction ; Mixed-valence complex ; Denitrification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The properties of the novel copper enzyme nitrous oxide reductase from denitrifyingPseudomonas stutzeri are described. Multifrequency electron paramagnetic resonance spectroscopy is used to characterize the various forms of the enzyme. The features observed at 2.4, 3.4, 4.5, 9.31 and 35 GHz are explained by a mixed-valence \s[Cu(1.5)\3. Cu(1.5)\s]S=\12 species with the unpaired electron delocalized between the two Cu nuclei. This site is also present in the catalytically inactive derivative of nitrous oxide reductase which was obtained from a transposon Tn5-induced mutant with defective chromophore biosynthesis. The resemblance of the low-frequency electron paramagnetic resonance spectra to the spectra for the so-called CuA of cytochromec oxidase can be taken as a first indication that the CuA may have a structural and electronic arrangement similar to the electron-paramagnetic-resonance-detectable copper in nitrous oxide reductase. Results from oxidation/reduction experiments, and from a quantitative determination of sulfhydryl and disulfide residues in the various forms of nitrous oxide reductase, suggest the involvement of the redox-couple cysteine/cystine in the structural organization of the active site of nitrous oxide reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01179514
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  • 2
    Electronic Resource
    Electronic Resource
    Mechanism of dissimilatory sulfite reduction by Desulfovibrio desulfuricans: purification of a membrane-bound sulfite reductase and coupling with cytochrome c3 and hydrogenase (1994)
    Springer
    Archives of microbiology 162 (1994), S. 255-260 
    Details
    ISSN: 1432-072X
    Keywords: Key words     Sulfite reductase ; Desulfoviridin ; Membranes ; Carbon monoxide ; Reconstitution ; Cytochrome c3 ; Hydrogenase ; Ion chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract      The localization of the dissimilatory sulfite reductase in Desulfovibrio desulfuricans strain Essex 6 was investigated. After treatment of the cells with lysozyme, 90% of the sulfite reductase activity was found in the membrane fraction, compared to 30% after cell rupture with the French press. Sulfite reductase was purified from the membrane (mSiR) and the soluble (sSiR) fraction. On SDS-PAGE, both mSiR and sS iR exhibited three bands at 50, 45 and 11 kDa, respectively. From their UV/VIS properties (distinct absorption maxima at 391, 410, 583, 630 nm, enzymes as isolated) and the characteristic red fluorescence in alkaline solution, mSiR and sSiR were identified as desulfoviridin. Sulfite reductase (HSO3 –→H2S) activity was reconstituted by coupling of mSiR to hydrogenase and cytochrome c 3 from D. desulfuricans. The specific activity of mSiR was 103 nmol H2 min–1 mg–1, and sulfide was the major product (72% of theoretical yield). No coupling was found with sSiR under these conditions. Furthermore, carbon monoxide was used to differentiate between the membrane-bound and the soluble sulfite reductase. In a colorimetric assay, with photochemically reduced methyl viologen as redox mediator, CO stimulated the activity of sSiR significantly. CO had no effect in the case of mSiR. These studies documented th at, as isolated, both forms of sulfite reductase behaved differently in vitro. Clearly, in D. desulfuricans, the six electron conversion HSO3 –→H2S was achieved by a membrane-bound desulfoviridin without the assistance of artificial redox mediators, such as methyl viologen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301847
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Mechanism of dissimilatory sulfite reduction by Desulfovibrio desulfuricans: purification of a membrane-bound sulfite reductase and coupling iwth cytochrome c 3 and hydrogenase (1994)
    Springer
    Archives of microbiology 162 (1994), S. 255-260 
    Details
    ISSN: 1432-072X
    Keywords: Sulfite reductase ; Desulfoviridin Membranes ; Carbon monoxide ; Reconstitution Cytochrome c 3 ; Hydrogenase ; Ion chromatography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The localization of the dissimilatory sulfite reductase in Desulfovibrio desulfuricans strain Essex 6 was investigated. After treatment of the cells with lysozyme, 90% of the sulfite reductase activity was found in the membrane fraction, compared to 30% after cell rupture with the French press. Sulfite reductase was purified from the membrane (mSiR) and the soluble (sSiR) fractiion. On SDS-PAGE, both mSiR and sSiR exhibited three bands at 50, 45 and 11 kDa, respectively. From their UV/VIS properties (distinct absorption maxima at 391, 410, 583, 630 nm, enzymes as isolated) and the characteristic red fluorescence in alkaline solution, mSiR and sSiR were identified as desulfoviridin. Sulfite reductase (HSO3 -→H2S) activity was reconstituted by coupling of mSiR to hydrogenase and cytochrome c 3 from D. desulfuricans. The specific activity of mSiR was 103 nmol H2 min-1 mg-1, and sulfide was the major product (72% of theoretical yield). No coupling was found with sSiR under these conditions. Furthermore, carbon monoxide was used to diferentiate between the membrane-bound and the soluble sulfite reductase. In a colorimetric assay, with photochemically reduced methyl viologen as redox mediator, CO stimulated the activity of sSiR significantly. CO had no effect in the case of mSiR. These studies documented that, as isolated, both forms of sulfite reductase behaved differently in vitro. Clearly, in D. desulfuricans, the six electron conversion HSO3 -→H2S was achieved by a membranebound desulfoviridin without the assistance of artificial redox mediators, such as methyl viologen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00301847
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    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Probing the ground state of the purple mixed valence CuA center in nitrous oxide reductase: a CW ENDOR (X-band) study of the 65Cu, 15N-histidine labeled enzyme and interpretation of hyperfine couplings by molecular orbital calculations (1998)
    Springer
    JBIC 3 (1998), S. 53-67 
    Details
    ISSN: 1432-1327
    Keywords: Key words  Endor ; CuA ; Molecular orbital theory ; Hyperfine coupling ; Spin density ; Enzymes Nitrous oxide reductase (EC 1.7.99.6) ; cytochrome c oxidoreductase (EC 1.9.3.1)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  CW ENDOR (X-band) spectra for the purple mixed-valence [Cu(1.5+)...Cu(1.5+)], S = 1/2, CuA site in nitrous oxide reductase were obtained after insertion of 65Cu or both 65Cu and 15N-histidine. The 14N/15N isotopic substitution allowed for an unambiguous deconvolution of proton and nitrogen hyperfine couplings in the spectra. A single nitrogen coupling with a value of 12.9 ± 0.4 MHz for 14N was detected. Its anisotropy was characteristic for imidazole bound to copper. A spin density of 3–5% was estimated for the nitrogen donors to CuA, indicating that the ground state is 2B3u. Proton hyperfine structure was detected from four Cβ protons of coordinating cysteine residues. Their isotropic and anisotropic parts were deconvoluted by spectral simulation. From the anisotropic couplings a spin density of 16–24% was estimated for each of the cysteine thiolate donors of CuA. The [NHisCu(RS)2CuNHis]+ core structure of CuA in nitrous oxide reductase from Pseudomonas stutzeri is predicted to be similar to the crystallographically determined CuA* structure (Wilmanns M, Lappalainen P, Kelly M, Sauer-Eriksson E, Saraste M (1995) Proc Natl Acad Sci USA 92 : 11955–11959), but distinct from the CuA structure of Paracoccus denitrificans cytochrome c oxidase (Iwata S, Ostermeier C, Ludwig B, Michel H (1995) Nature 376 : 660–669). The angular dependence of the isotropic couplings as a function of the electronic ground state was calculated by the INDO/S method. The Mulliken atomic-spin populations calculated by a gradient-corrected density functional method and the semiempirical INDO/S method were compared with experimentally derived spin populations, and good agreement between theory and experiment was found for both calculations. The ground state of CuA is best represented by the resonance structures of the form [CuIS–S–CuII↔ CuIS•S–CuI↔ CuIS–S•CuI↔ CuIIS–S–CuI]. It is proposed that the Cu 4s,p as well as sulfur 3d orbitals play a role in the stabilization of this novel type of cluster.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010649
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    Paper (German National Licenses)
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