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Temporary Storage for Electrons in a Hydrogen-Producing Enzyme

posted Nov 4, 2012, 2:31 PM by Jose L. Mendoza-Cortes
ScienceDaily (Nov. 2, 2012) — Scientists at the Max Planck Institute for Chemical Energy Conversion (MPI CEC) and the Ruhr-Universität Bochum (RUB) have found through spectroscopic investigations on a hydrogen-producing enzyme that the environment of the catalytic site acts as an electron reservoir in the enzyme. Thus, it can very efficiently produce hydrogen, which has great potential as a renewable energy source. The research team describes their results in the journal Angewandte Chemie.
[Credit] The images shows the NiFe center but the general features are present in the FeFe hydrogenases [Link]. 

Producing hydrogen with enzymes

The system analysed constitutes an enzyme that catalyses the formation and conversion of hydrogen. In its centre it has a double-iron core, and is therefore also called [FeFe] hydrogenase. Hydrogenases are of great interest for energy research, since they can efficiently produce hydrogen. However, new catalysts can only be developed given a deep understanding of their mode of action.
Electron transfer in several steps

In hydrogen production, two electrons get together with two protons. The research team showed that, as expected, the first electron is initially transferred to the iron centre of the enzyme. The second transfer on the other hand is to an iron-sulphur cluster that is located in the periphery. It thus forms a temporary storage for the second electron. This "super-reduced" state may be responsible for the extremely high efficiency of the hydrogenase. Subsequently both electrons are transferred in one step from the enzyme to the protons, so that hydrogen is generated.

"Only the use of two different spectroscopic techniques made the discovery possible," says Agnieszka Adamska, a doctoral student at MPI CEC who carried out the spectroscopic studies.

10,000 molecules of hydrogen per second

"Up to 10,000 molecules of hydrogen per second can be generated by a single [FeFe] centre," says Camilla Lambertz, a postdoc at the RUB [...]