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Discriminating changes in intracellular NADH/NAD+ levels due to anoxicity and H2 supply in R. eutropha cells using the Frex fluorescence sensor

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  • S. Wilkening
  • F. J. Schmitt
  • O. Lenz
  • I. Zebger
  • M. Horch
  • T. Friedrich


Publication details

JournalBiochimica et Biophysica Acta - Bioenergetics
DateAccepted/In press - 10 Aug 2019
DateE-pub ahead of print - 13 Aug 2019
DatePublished (current) - 1 Oct 2019
Issue number10
Number of pages9
Early online date13/08/19
Original languageEnglish


The hydrogen-oxidizing “Knallgas” bacterium Ralstonia eutropha can thrive in aerobic and anaerobic environments and readily switches between heterotrophic and autotrophic metabolism, making it an attractive host for biotechnological applications including the sustainable H2-driven production of hydrocarbons. The soluble hydrogenase (SH), one out of four different [NiFe]-hydrogenases in R. eutropha, mediates H2 oxidation even in the presence of O2, thus providing an ideal model system for biological hydrogen production and utilization. The SH reversibly couples H2 oxidation with the reduction of NAD+ to NADH, thereby enabling the sustainable regeneration of this biotechnologically important nicotinamide cofactor. Thus, understanding the interaction of the SH with the cellular NADH/NAD+ pool is of high interest. Here, we applied the fluorescent biosensor Frex to measure changes in cytoplasmic [NADH] in R. eutropha cells under different gas supply conditions. The results show that Frex is well-suited to distinguish SH-mediated changes in the cytoplasmic redox status from effects of general anaerobiosis of the respiratory chain. Upon H2 supply, the Frex reporter reveals a robust fluorescence response and allows for monitoring rapid changes in cellular [NADH]. Compared to the Peredox fluorescence reporter, Frex displays a diminished NADH affinity, which prevents the saturation of the sensor under typical bacterial [NADH] levels. Thus, Frex is a valuable reporter for on-line monitoring of the [NADH]/[NAD+] redox state in living cells of R. eutropha and other proteobacteria. Based on these results, strategies for a rational optimization of fluorescent NADH sensors are discussed.

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© 2019 Elsevier B.V. All rights reserved. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy.

    Research areas

  • Fluorescence sensor protein, Frex, Light-driven bio-hydrogen production, NAD, NADH, R. eutropha, Redox sensing, Soluble hydrogenase

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