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@ARTICLE{Martini:471645,
      author       = {Martini, Maria and Ruediger, Olaf and Breuer, Nina and
                      Nöring, Birgit and DeBeer, Serena and Rodriguez Macia,
                      Patricia and Birrell, James},
      editor       = {Bren, Kara},
      title        = {{T}he {N}onphysiological {R}eductant {S}odium {D}ithionite
                      and [{F}e{F}e] {H}ydrogenase: {I}nfluence on the {E}nzyme
                      {M}echanism},
      journal      = {Journal of the American Chemical Society},
      volume       = {143},
      number       = {43},
      issn         = {0002-7863},
      address      = {Washington, DC},
      publisher    = {American Chemical Society},
      reportid     = {PUBDB-2021-04513, I-20200084},
      pages        = {18159 - 18171},
      year         = {2021},
      abstract     = {[FeFe] hydrogenases are highly active enzymes for
                      interconverting protons and electrons with hydrogen (H$_2$).
                      Their active site H-cluster is formed of a canonical
                      [4Fe-4S] cluster ([4Fe-4S]$_H$) covalently attached to a
                      unique [2Fe] subcluster ([2Fe]$_H$), where both sites are
                      redox active. Heterolytic splitting and formation of H$_2$
                      takes place at [2Fe]$_H$, while [4Fe-4S]$_H$ stores
                      electrons. The detailed catalytic mechanism of these enzymes
                      is under intense investigation, with two dominant models
                      existing in the literature. In one model, an alternative
                      form of the active oxidized state H$_{ox}$, named H$_{ox}$H,
                      which forms at low pH in the presence of the
                      nonphysiological reductant sodium dithionite (NaDT), is
                      believed to play a crucial role. H$_{ox}$H was previously
                      suggested to have a protonated [4Fe-4S]$_H$. Here, we show
                      that H$_{ox}$H forms by simple addition of sodium sulfite
                      (Na$_2$SO$_3$, the dominant oxidation product of NaDT) at
                      low pH. The low pH requirement indicates that sulfur dioxide
                      (SO$_2$) is the species involved. Spectroscopy supports
                      binding at or near [4Fe-4S]$_H$, causing its redox potential
                      to increase by ∼60 mV. This potential shift detunes the
                      redox potentials of the subclusters of the H-cluster,
                      lowering activity, as shown in protein film electrochemistry
                      (PFE). Together, these results indicate that H$_{ox}$H and
                      its one-electron reduced counterpart H$_{red}$'H are
                      artifacts of using a nonphysiological reductant, and not
                      crucial catalytic intermediates. We propose renaming these
                      states as the "dithionite (DT) inhibited" states
                      H$_{ox}$-DT$_i$ and H$_{red}$-DT$_i$. The broader potential
                      implications of using a nonphysiological reductant in
                      spectroscopic and mechanistic studies of enzymes are
                      highlighted.},
      cin          = {DOOR ; HAS-User / MPG},
      ddc          = {540},
      cid          = {I:(DE-H253)HAS-User-20120731 / I:(DE-H253)MPG-20120806},
      pnm          = {6G3 - PETRA III (DESY) (POF4-6G3) / FS-Proposal: I-20200084
                      (I-20200084)},
      pid          = {G:(DE-HGF)POF4-6G3 / G:(DE-H253)I-20200084},
      experiment   = {EXP:(DE-H253)P-P01-20150101},
      typ          = {PUB:(DE-HGF)16},
      pubmed       = {pmid:34668697},
      UT           = {WOS:000715845900034},
      doi          = {10.1021/jacs.1c07322},
      url          = {https://bib-pubdb1.desy.de/record/471645},
}