Waldeck, A. Reginald and Stowell, Michael H. B. and Lee, Hung Kay and Hung, Shao-Ching and Matsson, Mikael and Hederstedt, Lars and Ackrel, Brian A. C. and Chan, Sunney I. (1997) Electron Paramagnetic Resonance Studies of Succinate:Ubiquinone Oxidoreductase from Paracoccus denitrificans. Journal of Biological Chemistry, 272 (31). pp. 19373-19382. ISSN 0021-9258. http://resolver.caltech.edu/CaltechAUTHORS:20120125-131713605
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Electron paramagnetic resonance (EPR) studies of succinate:ubiquinone oxidoreductase (SQR) from Paracoccus denitrificans have been undertaken in the purified and membrane-bound states. Spectroscopic “signatures” accounting for the three iron-sulfur clusters (2Fe-2S, 3Fe-4S, and 4Fe-4S), cytochromeb, flavin, and protein-bound ubisemiquinone radicals have been obtained in air-oxidized, succinate-reduced, and dithionite-reduced preparations at 4–10 K. Spectra obtained at 170 K in the presence of excess succinate showed a signal typical of that of a flavin radical, but superimposed with another signal. The superimposed signal originated from two bound ubisemiquinones, as shown by spectral simulations. Power saturation measurements performed on the air-oxidized enzyme provided evidence for a weak magnetic dipolar interaction operating between the oxidized 3Fe-4S cluster and the oxidized cytochrome b. Power saturation experiments performed on the succinate- and dithionite-reduced forms of the enzyme demonstrated that the 4Fe-4S cluster is coupled weakly to both the 2Fe-2S and the 3Fe-4S clusters. Quantitative interpretation of these power saturation experiments has been achieved through redox calculations. They revealed that a spin-spin interaction between the reduced 3Fe-4S cluster and the cytochrome b (oxidized) may also exist. These findings form the first direct EPR evidence for a close proximity (≤2 nm) of the high potential 3Fe-4S cluster, situated in the succinate dehydrogenase part of the enzyme, and the low potential, low spin b-heme in the membrane anchor of the enzyme.
|Additional Information:||© 1997 by The American Society for Biochemistry and Molecular Biology, Inc. Received for publication, March 17, 1997, and in revised form, May 14, 1997. We thank the late Dr. Vladimir Sled for valuable correspondence. Drs. Siegfried Musser and Brian Schultz are thanked for stimulating discussions and advice with EPR simulations, respectively. This work was funded in part by National Institutes of Health Grants GM 22432 (to S. I. C.) and HL-16251 (to B. A. C. A.) and a grant from the Swedish Natural Science Research Council (to L. H.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.|
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|Deposited By:||Tony Diaz|
|Deposited On:||16 Mar 2012 18:35|
|Last Modified:||16 Mar 2012 18:35|
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