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Researchers Discover a Previously Unknown Radical Signal in a Hydrogenase

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A man and a woman stand next to an electron paramagnetic resonance spectrometer in a laboratory. © TU Dortmund
The first shared authors with the EPR spectrometer: Melanie Heghmanns (TU Dortmund University) and Andreas Rutz (Ruhr University Bochum).

Hydrogen is considered as the fuel of the future. Hydrogenases are enzymes that optimize the reversible oxidation of molecular hydrogen and therefore serve as blueprints for green and cost-effective hydrogen production. However, their high sensitivity towards oxygen prevents their efficient use on an industrial scale. Researchers under the guidance of Junior Professor Müge Kasanmascheff from TU Dortmund University and Professor Thomas Happe from Ruhr University Bochum (RUB) have discovered a previously unknown radical signal in an exceptional oxygen-resistant hydrogenase. Their results suggest that the unknown radical signal might be responsible for the unique oxygen protection mechanism of this particular hydrogenase. Their work was recently published in the journal Chemical Science.

Hydrogenases are enzymes that are widely distributed in microorganisms and catalyze the evolution of molecular hydrogen. This reaction occurs at the active metal center, the so-called H-cluster, which is rapidly destroyed by oxygen. An oxygen-resistant exception is the [FeFe] hydrogenase of Clostridium beijerinckii (CbA5H), which can reversibly adopt a state protected from oxygen, as recently demonstrated by the RUB research team led by Thomas Happe, Professor of Photobiotechnology. The TU Dortmund team led by Junior Professor Müge Kasanmascheff then used electron paramagnetic resonance (EPR) spectroscopy to study the active site of CbA5H in more detail.

Studies with EPR Spectroscopy

EPR spectroscopy detects and characterizes unpaired electrons, for example, in transition metals and organic radicals. In addition to the known H-cluster states, the scientists discovered an unknown radical signal named R•ox. It differs in its properties from typical organic radicals and known H-cluster states. R•ox is mainly found in the oxidized enzyme and is only formed in the presence of the intact H-cluster and proton transfer pathway. Using selective 57Fe enrichment, the team managed to localize R•ox at or near the H cluster.

"The newly discovered radical signal is only formed in the presence of the active site and possibly part of a unique regulatory mechanism. Until the final elucidation of R•ox, we assume that the formation of the unknown radical signal is related to the special oxygen-protection mechanism of CbA5H," summarizes Junior Professor Müge Kasanmascheff.

The work was carried out within the framework of the RESOLV Cluster of Excellence, funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG).

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