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Photoinduced Electron Transfer Informs on Pathway Coupling in Flavin-Based Electron Bifurcation.

Seth A Wiley1, Carolyn E Lubner1

  • 1Biosciences Center, National Laboratory of the Rockies, Golden, Colorado 80401, United States.

ACS Bio & Med Chem Au
|February 23, 2026
PubMed
Summary

Flavin-based electron bifurcation (FBEB) uses the Nfn enzyme to create high-energy electrons. New cryogenic EPR methods reveal how this enzyme controls electron flow, offering insights into energy conversion.

Keywords:
Electron BifurcationEnzymesMechanismPhotochemistryProteinsReaction IntermediatesRedox Reactions

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Area of Science:

  • Biochemistry
  • Enzymology
  • Bioenergetics

Background:

  • Flavin-based electron bifurcation (FBEB) is a critical enzymatic process for energy conversion.
  • The NADH-dependent ferredoxin:NADP+-oxidoreductase (Nfn) enzyme in *Pyrococcus furiosus* utilizes FBEB to drive unfavorable reactions.
  • Understanding Nfn's mechanism for controlling high-energy electrons is crucial for bioenergetics research.

Purpose of the Study:

  • To investigate the mechanisms of electronic control in the low-potential pathway of Nfn.
  • To elucidate the role of the protein environment in managing short-lived, high-energy electron intermediates.
  • To gain insights into electron transfer steps and cofactor interactions within Nfn.

Main Methods:

  • Adaptation of low-temperature photoexcitation combined with electron paramagnetic resonance (EPR) spectroscopy.
  • Accumulation and characterization of short-lived radical intermediates at cryogenic temperatures.
  • Analysis of cofactor interactions, including [4Fe-4S] clusters, during electron bifurcation.

Main Results:

  • Observed coincident growth of radical intermediates and nearby [4Fe-4S] clusters upon NADPH illumination at cryogenic temperatures.
  • Photogenerated paramagnetic species were stable at liquid nitrogen temperatures and recombined upon warming.
  • Identified a potential gating mechanism involving key residue movement, influencing electron flow reversibility.

Conclusions:

  • The study provides novel insights into electron transfer dynamics and cofactor interactions in the Nfn low-potential pathway.
  • Cryogenic EPR successfully probes unstable intermediates, enhancing mechanistic understanding of FBEB.
  • A residue-based gating mechanism may regulate the directionality of electron flow in Nfn.