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  Pulsed Electron Paramagnetic Resonance Spectroscopy of 33S-Labeled Molybdenum Cofactor in Catalytically Active Bioengineered Sulfite Oxidase

Klein, E. L., Belaidi, A. A., Raitsimring, A. M., Davis, A. C., Krämer, T., Astashkin, A. V., et al. (2014). Pulsed Electron Paramagnetic Resonance Spectroscopy of 33S-Labeled Molybdenum Cofactor in Catalytically Active Bioengineered Sulfite Oxidase. Inorganic Chemistry, 53(2), 961-971. doi:10.1021/ic4023954.

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 Creators:
Klein, Eric L.1, 2, Author              
Belaidi, Abdel Ali3, Author
Raitsimring, Arnold M.1, Author
Davis, Amanda C.1, Author
Krämer, Tobias2, Author              
Astashkin, Andrei V.1, Author
Neese, Frank2, Author              
Schwarz, Günter3, Author
Enemark, John H.1, Author
Affiliations:
1Department of Chemistry and Biochemistry, The University of Arizona, 1306 E. University Boulevard, Tucson, Arizona 85721-0041, United States, ou_persistent22              
2Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society, ou_3023886              
3Institute of Biochemistry, University of Cologne, Zülpicher Strasse 47, 50674 Cologne, Germany, ou_persistent22              

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 Abstract: Molybdenum enzymes contain at least one pyranopterin dithiolate (molybdopterin, MPT) moiety that coordinates Mo through two dithiolate (dithiolene) sulfur atoms. For sulfite oxidase (SO), hyperfine interactions (hfi) and nuclear quadrupole interactions (nqi) of magnetic nuclei (I ≠ 0) near the Mo(V) (d1) center have been measured using high-resolution pulsed electron paramagnetic resonance (EPR) methods and interpreted with the help of density functional theory (DFT) calculations. These have provided important insights about the active site structure and the reaction mechanism of the enzyme. However, it has not been possible to use EPR to probe the dithiolene sulfurs directly since naturally abundant 32S has no nuclear spin (I = 0). Here we describe direct incorporation of 33S (I = 3/2), the only stable magnetic sulfur isotope, into MPT using controlled in vitro synthesis with purified proteins. The electron spin echo envelope modulation (ESEEM) spectra from 33S-labeled MPT in this catalytically active SO variant are dominated by the “interdoublet” transition arising from the strong nuclear quadrupole interaction, as also occurs for the 33S-labeled exchangeable equatorial sulfite ligand [Klein, E. L., et al. Inorg. Chem. 2012, 51, 1408−1418]. The estimated experimental hfi and nqi parameters for 33S (aiso = 3 MHz and e2Qq/h = 25 MHz) are in good agreement with those predicted by DFT. In addition, the DFT calculations show that the two 33S atoms are indistinguishable by EPR and reveal a strong intermixing between their out-of-plane pz orbitals and the dxy orbital of Mo(V).

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Language(s): eng - English
 Dates: 2013-09-212014-01-032014-01-21
 Publication Status: Published in print
 Pages: 11
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/ic4023954
 Degree: -

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Title: Inorganic Chemistry
  Abbreviation : Inorg. Chem.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 53 (2) Sequence Number: - Start / End Page: 961 - 971 Identifier: ISSN: 0020-1669
CoNE: https://pure.mpg.de/cone/journals/resource/0020-1669