[NiFe]-hydrogenases catalyze the interconversion of protons and hydrogen.  They have received attention for potential uses in both hydrogen production and utilization.  Uptake [NiFe]-hydrogenases from an array of species are effective electrocatalysts when adsorbed to pyrolytic graphite.  However, comparable attention has not been paid to other types of [NiFe]-hydrogenases.  We will present electrochemical investigations of two bidirectional [NiFe]-hydrogenases: HoxEFUYH from the cyanobacterium Synechocystis sp. PCC6803 and SHI from the anaerobic archaeon Pyrococcus furiosus.  Both enzymes are less biased toward hydrogen oxidation than their uptake cousins.  Additionally, both enzymes react differently with oxygen than the standard-uptake enzymes.  We will show that HoxEFUYH is oxygen-sensitive but can be reactivated in less than 90 seconds after exposure to oxygen.  On the other hand, PfSHI is oxygen-tolerant but forms two inactive states. Furthermore, the oxygen-tolerance of PfSHI cannot be explained by the same hypotheses put forward for oxygen-tolerant uptake enzymes.  Alternative explanations will be considered.

Bioelectrocatalysis by bidirectional [NiFe]-hydrogenases: Mechanistic comparison to uptake enzymes

243rd National Meeting (2012)

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