Pierre Ceccaldi, Marta Marques, Vincent Fourmond, Inês Cardoso Pereira and Christophe Léger
Chem. Commun., 2015, Accepted Manuscript DOI: 10.1039/C5CC05930E
Received 16 Jul 2015, Accepted 29 Jul 2015 First published online 30 Jul 2015
NiFeSe hydrogenases differ from standard NiFe hydrogenases by the replacement of one Ni-bound cysteine with selenocysteine. We used direct electrochemistry to characterize the kinetics of (in)activation of Desulfovibrio vulgaris Hildenborough NiFeSe hydrogenase under various conditions. We conclude that two oxidized inactive forms of the enzyme reductively reactivate at a significant rate, one much faster than the other, at potentials above the H+/H2 equilibrium potential. Both inactive states can be formed upon either aerobic or anaerobic oxidation, in a “CE” mechanism. We propose a resolution to the paradox that, in contrast with standard NiFe hydrogenases, spectroscopic studies of NiFeSe hydrogenase have not revealed any major signal attributable to Ni(III) states formed upon reaction with O2, despite the fact that two inactive states are formed under oxidizing conditions.