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Metalloenzymes in Biological Hydrogen Metabolism

Molecular hydrogen (H2) plays a pivotal role in the metabolism of many microorganisms, including bacteria, archaea and lower eukaryotes. Under strictly anoxic conditions, H2 is released as a waste product in the course of fermentative processes. H2 can also serve as valuable energy source when used in combination with suitable electron acceptors. Both reactions, H2 evolution through proton reduction and H2 oxidation to protons and electrons, are catalyzed by complex metalloenzymes referred to as hydrogenase. 

Catalysis takes place at transition metal centers displaying a sophisticated molecular architecture. Depending on the metal content of the active site, hydrogenases are classified into [Fe]-, [FeFe]-, and [NiFe]-hydrogenases. Besides their preferred substrate, H2, hydrogenases generally interact also with molecular oxygen (O2), which leads to the formation of (irreversibly) inactive forms of the catalytic center.

Life with explosive gas mixtures


Only few hydrogenases are able to perform H2 cycling in the presence of ambient O2. Prominent examples are the [NiFe]-hydrogenases of the “Knallgasbacterium” Ralstonia eutropha which are being investigated in our lab. R. eutropha couples H2 oxidation with the reduction of O2, a reaction that provides the cellular metabolism with plenty of energy and reducing power.

The catalytic conversion of H2 in the presence of O2 is a challenging process from different perspectives. However, the O2 tolerance of the Ralstonia hydrogenases is also highly attractive in terms of biotechnological application. Consequently, our research covers basic as well as applied aspects of these fascinating biocatalysts.

See "Projects" for details on our research.

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