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Oxygen-tolerant hydrogenases in biotechnology

The intriguing feature of the hydrogenases studied in our lab is their ability to operate in the presence of oxygen. This property is a fundamental prerequisite for their applicability in hydrogen technology.

Light-driven dihydrogen production

Lupe

We are using an interdisciplinary approach in order to generate molecular hydrogen as an alternative fuel from light an water. Three complex biocatalysts are involved in the corresponding overall process, namely photosystem I (PS I), photosystem II (PS II) and O2-tolerant hydrogenase. By genetic engineering we have fused a hydrogenase from R. eutropha directly to the acceptor site of PS I from Synechocystis PCC 6803. The resulting hydrogenase-PS I protein complex showed high H2 production rates in light-dependent manner. Currently we are working on the genetic transfer of the modified hydrogenase genes into cyanobacteria. An O2-tolerant hydrogenase should withstand the O2 produced by PS II, resulting in a living cell that produces H2 directly from light and water.

Our current research concentrates on the improvement of the hydrogenase-photosystem complex by applying alternative O2-tolerant hydrogenases and coupling strategies. Furthermore we aim at the heterologous production of active O2-tolerant hydrogenase in cyanobacteria.

Enzyme-based fuel cell

Lupe

Another promising technological application, which is also based on the exceptional tolerance towards O2 and CO of the [NiFe]-hydrogenases, is the development of enzyme-based fuel cells. In close collaboration with K. Vincent and F. Armstrong (University of Oxford), we have constructed a prototypical biological fuel cell that is equipped with enzyme-coated pyrolytic carbon strips instead of the conventional platinum electrodes. At the hydrogenase-covered anode, H2 is split into electrons (e-) and protons (H+) whereas the reaction catalyzed at cathode oxygen re-uses the electrons and protons to reduce molecular oxygen (O2) to water. The latter reaction is mediated by the fungal enzyme laccase. These processes result in charge separation which induces an electric current. The biofuel cell remains functional at very low hydrogen concentrations, such as 3% H2 in air, and does not require a membrane-based separation of the compartments.

NAD(P)H cofactor regeneration

Due to its high catalytic activity and superb O2 tolerance, the SH of R. eutropha represents a promising cofactor regeneration system that produces NADH from H2 under aerobic conditions. Several industrially relevant enzyme-driven syntheses, such as the production of L-tert leucine, require continuous replenishment of NADH. Current investigations in collaboration with Marion Ansorge-Schumacher (TU Dresden) and Kylie Vincent (Oxford University) aim at the installation of SH as a promising alternative to the industrially used enzyme formate dehydrogenase.

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