EPR and 57Fe ENDOR investigation of 2Fe ferredoxins from Aquifex aeolicus

George E. Cutsail, Peter E. Doan, Brian M. Hoffman, Jacques Meyer, Joshua Telser*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


We have employed EPR and a set of recently developed electron nuclear double resonance (ENDOR) spectroscopies to characterize a suite of [2Fe-2S] ferredoxin clusters from Aquifex aeolicus (Aae Fd1, Fd4, and Fd5). Antiferromagnetic coupling between the FeII, S = 2, and Fe III, S = 5/2, sites of the [2Fe-2S]+ cluster in these proteins creates an S = 1/2 ground state. A complete discussion of the spin-Hamiltonian contributions to g includes new symmetry arguments along with references to related FeS model compounds and their symmetry and EPR properties. Complete 57Fe hyperfine coupling (hfc) tensors for each iron, with respective orientations relative to g, have been determined by the use of "stochastic" continuous wave and/or "random hopped" pulsed ENDOR, with the relative utility of the two approaches being emphasized. The reported hyperfine tensors include absolute signs determined by a modified pulsed ENDOR saturation and recovery (PESTRE) technique, RD-PESTRE - a post-processing protocol of the "raw data" that comprises an ENDOR spectrum. The 57Fe hyperfine tensor components found by ENDOR are nicely consistent with those previously found by Mössbauer spectroscopy, while accurate tensor orientations are unique to the ENDOR approach. These measurements demonstrate the capabilities of the newly developed methods. The high-precision hfc tensors serve as a benchmark for this class of FeS proteins, while the variation in the 57Fe hfc tensors as a function of symmetry in these small FeS clusters provides a reference for higher-nuclearity FeS clusters, such as those found in nitrogenase.

Original languageEnglish (US)
Pages (from-to)1137-1150
Number of pages14
JournalJournal of Biological Inorganic Chemistry
Issue number8
StatePublished - Dec 2012


  • Hyperfine coupling
  • Iron-sulfur proteins
  • Ligand field theory
  • Magnetic resonance

ASJC Scopus subject areas

  • Biochemistry
  • Inorganic Chemistry


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