Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany
Xi Chen
Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany
Katharina Spengler
Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany
Karoline Terberger
Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany
Marko Boehm
Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany; Department of Molecular Plant Physiology, Bioenergetics in Photoautotrophs, University of Kassel, Kassel, Germany
Jens Appel
Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany; Department of Molecular Plant Physiology, Bioenergetics in Photoautotrophs, University of Kassel, Kassel, Germany
Thomas Barske
Plant Physiology Department, University of Rostock, Rostock, Germany
Department of Biology, Botanical Institute, Christian-Albrechts-University, Kiel, Germany; Department of Molecular Plant Physiology, Bioenergetics in Photoautotrophs, University of Kassel, Kassel, Germany
The decarboxylation of pyruvate is a central reaction in the carbon metabolism of all organisms. It is catalyzed by the pyruvate:ferredoxin oxidoreductase (PFOR) and the pyruvate dehydrogenase (PDH) complex. Whereas PFOR reduces ferredoxin, the PDH complex utilizes NAD+. Anaerobes rely on PFOR, which was replaced during evolution by the PDH complex found in aerobes. Cyanobacteria possess both enzyme systems. Our data challenge the view that PFOR is exclusively utilized for fermentation. Instead, we show, that the cyanobacterial PFOR is stable in the presence of oxygen in vitro and is required for optimal photomixotrophic growth under aerobic and highly reducing conditions while the PDH complex is inactivated. We found that cells rely on a general shift from utilizing NAD(H)- to ferredoxin-dependent enzymes under these conditions. The utilization of ferredoxins instead of NAD(H) saves a greater share of the Gibbs-free energy, instead of wasting it as heat. This obviously simultaneously decelerates metabolic reactions as they operate closer to their thermodynamic equilibrium. It is common thought that during evolution, ferredoxins were replaced by NAD(P)H due to their higher stability in an oxidizing atmosphere. However, the utilization of NAD(P)H could also have been favored due to a higher competitiveness because of an accelerated metabolism.
