Communication of the H2-activating site with various protein and redox modules of [NiFe] hydrogenases

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A key energy-rich substrate for microbial metabolism is molecular hydrogen. Enzymatic conversion of H2 into electrons and protons, catalyzed by hydrogenase, is considered as an early mode of energy coupling which may have been evolved in ancient organisms. The data expected from the genetic, biochemical and spectroscopic experiments proposed in this project will lay the groundwork for mapping bidirectional electron and proton transfer pathways from and to the H2 activating NiFe-metallocenter and various acceptor/donor molecules. Coordination between electron and proton transfer, import and export reactions that are guided through either common or separate channels and finally control mechanisms that steer the flow of electrons either towards H2 uptake or H2 production are investigated with the cytoplasmic NAD-reducing hydrogenase of Alcaligenes eutrophus. Direct coupling of H2 oxidation with components of the respiratory chain are analyzed with the membrane-bound hydrogenase of A. eutrophus. The selected models are significant in particular since [NiFe] hydrogenases are composed of elementary functional modules that are conserved in other multi-electron redox enzymes such as the mitochondrial complex I.