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The light-induced Ni-C to Ni-L transition results in the dissociation of a hydrogenic species, originating from the dihydrogen splitting at the active site. Back conversion in the dark to form Ni-C was investigated by studying the rebinding kinetics of this ligand in protonated (H(2)/H(2)O) and deuterated (D(2)/D(2)O) samples using time resolved FTIR spectroscopy.

Background: Cyanobacterial uptake hydrogenases perform hydrogen oxidation in nitrogen-fixing cyanobacteria, but their biophysical properties are unknown. Results: The small subunit, HupS, from the Nostoc punctiforme uptake hydrogenase was heterologously expressed and spectroscopically characterized in different redox conditions. Conclusion: Recombinant HupS incorporates three iron-sulfur clusters with unusual iron coordination. Significance: We provide the foundation for engineering of cyanobacterial uptake hydrogenases.

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