Equilibrium and Ultrafast Kinetic Studies Manipulating Electron Transfer: A Short-Lived Flavin Semiquinone is Not Sufficient for Electron Bifurcation

Paul King, Carolyn Lubner, Paul King, John Hoben, Gerrit Schut, Diep Nguyen, Karl Hempel, Michael Adams, Anne-Frances Miller, Paul King, Paul King, Paul King

Research output: Contribution to journalArticlepeer-review

19 Scopus Citations


Flavin-based electron transfer bifurcation is emerging as a fundamental and powerful mechanism for conservation and deployment of electrochemical energy in enzymatic systems. In this process, a pair of electrons is acquired at intermediate reduction potential (i.e. intermediate reducing power), and each electron is passed to a different acceptor, one with lower and the other with higher reducing power, leading to "bifurcation." It is believed that a strongly reducing semiquinone species is essential for this process, and it is expected that this species should be kinetically short-lived. We now demonstrate that the presence of a short-lived anionic flavin semiquinone (ASQ) is not sufficient to infer the existence of bifurcating activity, although such a species may be necessary for the process. We have used transient absorption spectroscopy to compare the rates and mechanisms of decay ofASQgenerated photochemically in bifurcating NADH-dependent ferredoxin-NADP+ oxidoreductase and the non-bifurcating flavoproteins nitroreductase, NADH oxidase, and flavodoxin. We found that different mechanisms dominate ASQ decay in the different protein environments, producing lifetimes ranging over 2 orders of magnitude. Capacity for electron transfer among redox cofactors versus charge recombination with nearby donors can explain the range of ASQ lifetimes that we observe. Our results support a model wherein efficient electron propagation can explain the short lifetime of the ASQ of bifurcating NADH-dependent ferredoxin-NADP+ oxidoreductase I and can be an indication of capacity for electron bifurcation.

Original languageAmerican English
Pages (from-to)14039-14049
Number of pages11
JournalJournal of Biological Chemistry
Issue number34
StatePublished - 25 Aug 2017

NREL Publication Number

  • NREL/JA-2700-68454


  • electron bifurcation
  • electron transfer
  • energetics
  • flavin
  • flavoprotein
  • fluorescence
  • transient absorption spectrocopy


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