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  • 1
    Electronic Resource
    Electronic Resource
    The membrane-bound high-molecular-mass cytochromes c from Desulfovibrio gigas and Desulfovibrio vulgaris Hildenborough; EPR and Mössbauer studies (1997)
    Springer
    JBIC 2 (1997), S. 23-31 
    Details
    ISSN: 1432-1327
    Keywords: Key words Multiheme cytochrome c ; Desulfovibrio ; Membrane proteins ; Electron transfer ; EPR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The high-molecular-mass cytochromes c (Hmcs) from the sulfate-reducing bacteria Desulfovibrio gigas and Desulfovibrio vulgaris (Hildenborough) were found to be strongly bound to the cytoplasmic membrane. After detergent solubilization they were shown to be water soluble and to be similar to those previously isolated from the soluble fractions in terms of N-terminal sequence, molecular mass, UV-visible and EPR spectroscopies. In D. gigas, higher amounts of Hmc can be obtained from the membranes than from the soluble fraction. This enabled further characterization of both cytochromes. The apparent heme reduction potentials of both Hmcs, determined at pH 7.5 through visible and EPR redox titrations, span a large range of redox potentials, approximately between 0 and –280 mV, and can be roughly divided into three groups: four to five hemes have E 0s of –30 mV to –100 mV, three to four hemes have E 0s around –170 mV, and seven to eight hemes have a lower E 0 of –250 to –280 mV. Several of these redox potentials are strongly pH dependent. Mössbauer studies of oxidized and reduced D. vulgaris Hmc show that this protein contains two high-spin hemes in both oxidation states. The rate of reduction of both Hmcs with the periplasmic hydrogenases from the corresponding organisms is extremely slow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050102
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  • 2
    Electronic Resource
    Electronic Resource
    Redox-Bohr effect in electron/proton energy transduction: cytochrome c 3 coupled to hydrogenase works as a 'proton thruster' in Desulfovibrio vulgaris (1997)
    Springer
    JBIC 2 (1997), S. 488-491 
    Details
    ISSN: 1432-1327
    Keywords: Key words Cytochrome c3 ; Electron transfer ; Proton transfer ; Redox-Bohr ; Energy transduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  A central step in the metabolism of Desulfovibrio spp. is the oxidation of molecular hydrogen catalyzed by a periplasmic hydrogenase. However, this enzymatic activity is quite low at physiological pH. The hypothesis that, in the presence of the tetrahaem cytochrome c 3, hydrogenase can maintain full activity at physiological pH through the concerted capture of the resulting electrons and protons by the cytochrome was tested for the case of Desulfovibrio vulgaris (Hildenborough). The crucial step involves an electron-to-proton energy transduction, and is achieved through a network of cooperativities between redox and ionizable centers within the cytochrome (redox-Bohr effect). This mechanism, which requires a relocation of the proposed proton channel in the hydrogenase structure, is similar to that proposed for the transmembrane proton pumps, and is the first example which shows evidence of functional energy transduction in the absence of a membrane confinement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050160
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of cytochrome c 6 from the cyanobacterium Anabaena PCC 7119 (1997)
    Springer
    JBIC 2 (1997), S. 225-234 
    Details
    ISSN: 1432-1327
    Keywords: Key words Cytochrome c6 ; Anabaena PCC 7119 ; EPR ; NMR ; Redox-Bohr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  A soluble monoheme c–type cytochrome c 6 has been isolated from the cyanobacterium Anabaena PCC 7119. It is a basic protein, with a molecular mass of 9.7 kDa, which accepts electrons from Anabaena ferredoxin in the ferredoxin-NADP+reductase-dependent NADPH cytochrome c reductase activity assay. The turnover of the reaction has an optimum pH at 7.5. Flavodoxin can also replace ferredoxin in this assay, but with only 20% efficiency. Plastocyanin from Anabaena PCC 7119, as well as the c 6 cytochromes from the green algae Chlorella fusca and Monoraphidium braunii are also shown to accept electrons from Anabaena ferredoxin. The reduction potential of cytochrome c 6 at pH 6.7 was determined to be 338 mV and is pH dependent, with pK a ox=8.4±0.1 and pK a red≈9.5. The ferric and ferrous cytochrome forms and their pH equilibria have been studied using visible, EPR and 1H-NMR spectroscopies. The amino acid sequence and the visible and NMR spectroscopic data indicate that the heme iron has a methionine-histidine axial coordination in the pH range 5–11. However, the EPR data for the ferricytochrome are complex and show that in this pH range five distinct forms are present. Between pH 5 and 9 the spectrum is dominated by two rhombic species, with g–values at 2.94, 2.29, 1.43 and at 2.84, 2.34, 1.56, which interconvert with a pK a of 8.4. The NMR data also show a main interconversion between two cytochrome forms at this pH, which coincides with that determined from the pH dependence of the reduction potential. Both these forms were associated with a methionine-histidine heme-iron coordination by correlation with the visible and NMR spectral data, although having crystal field parameters atypical for this type of coordination. Anabaena cytochrome c 6 is one more example of a heme protein for which the widely used crystal field analysis of the EPR data (truth diagram) fails to unequivocally determine the type of heme-iron ligation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050128
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  • 4
    Electronic Resource
    Electronic Resource
    Electron transfer between hydrogenases and mono- and multiheme cytochromes in Desulfovibrio ssp (1998)
    Springer
    JBIC 3 (1998), S. 494-498 
    Details
    ISSN: 1432-1327
    Keywords: Key words Desulfovibrio ; Cytochrome c ; Hydrogenase ; Electron transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  A comparative study of electron transfer between the 16 heme high molecular mass cytochrome (Hmc) from Desulfovibrio vulgaris Hildenborough and the [Fe] and [NiFe] hydrogenases from the same organism was carried out, both in the presence and in the absence of catalytic amounts of cytochrome c 3. For comparison, this study was repeated with the [NiFe] hydrogenase from D. gigas. Hmc is very slowly reduced by the [Fe] hydrogenase, but faster by either of the two [NiFe] hydrogenases. In the presence of cytochrome c 3, in equimolar amounts to the hydrogenases, the rates of electron transfer are significantly increased and are similar for the three hydrogenases. The results obtained indicate that the reduction of Hmc by the [Fe] or [NiFe] hydrogenases is most likely mediated by cytochrome c 3. A similar study with D. vulgaris Hildenborough cytochrome c 553 shows that, in contrast, this cytochrome is reduced faster by the [Fe] hydrogenase than by the [NiFe] hydrogenases. However, although catalytic amounts of cytochrome c 3 have no effect in the reduction by the [Fe] hydrogenase, it significantly increases the rate of reduction by the [NiFe] hydrogenases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s007750050259
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