Accumulating the hydride state in the catalytic cycle of [FeFe]-hydrogenases

This is the authors' abstract. We don't add key points for this paper.

H 2 turnover at the [FeFe]-hydrogenase cofactor (H-cluster) is assumed to follow a reversible heterolytic mechanism, first yielding a proton and a hydrido-species which again is double-oxidized to release another proton. Three of the four presumed catalytic intermediates (H ox , H red /H red and H sred ) were characterized, using various spectroscopic techniques. However, in catalytically active enzyme, the state containing the hydrido-species, which is eponymous for the proposed heterolytic mechanism, has yet only been speculated about. We use different strategies to trap and spectroscopically characterize this transient hydride state (H hyd ) for three wild-type [FeFe]-hydrogenases. Applying a novel set-up for real-time attenuated total-reflection Fourier-transform infrared spectroscopy, we monitor compositional changes in the state-specific infrared signatures of [FeFe]-hydrogenases, varying buffer pH and gas composition. We selectively enrich the equilibrium concentration of H hyd , applying Le Chatelier’s principle by simultaneously increasing substrate and product concentrations (H 2 /H + ). Site-directed manipulation, targeting either the proton-transfer pathway or the adt ligand, significantly enhances H hyd accumulation independent of pH.