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Mössbauer spectroscopy on the reaction center of Rhodopseudomonas viridis

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Fritzsch,  Günter
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Sinning,  Irmgard Maria
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Michel,  Hartmut
Department of Molecular Membrane Biology, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Frolov, E. N., Birk, A., Fritzsch, G., Sinning, I. M., Michel, H., Goldanskii, V. I., et al. (1991). Mössbauer spectroscopy on the reaction center of Rhodopseudomonas viridis. Hyperfine Interactions, 68(1), 59-69. doi:10.1007/BF02396452.


Cite as: http://hdl.handle.net/21.11116/0000-0007-1D7E-D
Abstract
Proteins called “reaction centers” (RC) can be isolated from many photosynthetic bacteria. They have one non-heme iron in a quinone acceptor region. The RC of Rhodopseudomonas viridis contains an additional tightly bound tetra-heme cytochrome c subunit. The electronic configuration of both cytochrome and the non-heme iron has been studied in the crystallized protein by Mössbauer spectroscopy at different redox potentials, pH-values, and with an addition of o-phenanthroline. At high potentials (Eh=+500mV) all heme irons are in the low spin Fe3+-state, and at low potential (Eh=−150mV) they are low spin Fe2+ with the same Mössbauer parameters for all hemes independent of pH. Redox titrations change the relative area of the reduced and oxidized states in agreement with other methods. The non-heme iron shows a high spin Fe2+ configuration independent of Eh and pH with parameters comparable to those of Rhodopseudomonas sphaeroides. Surprisingly, there is strong evidence for another non-heme iron species in part of the molecules with a Fe2+ low spin configuration. Incubation with o-phenanthroline decreases the relative Fe2+ hs-area and increases the contribution of Fe2+ ls-area. Above 210K the mean square displacement, [x2], of the RC-crystals increases more than linearly with temperature. This may be correlated with the increase of the electron transfer rate and indicates that intramolecular mobility influences the functional activity of a protein.