Transforming an oxygen-tolerant [NiFe] uptake hydrogenase into a proficient, reversible hydrogen producer

Many hydrogenases are highly electroactive when attached to an electrode, and most exhibit reversible 2H super(+)/H sub(2) electrocatalysis, i.e.only a minuscule overpotential is required to drive the reaction in either direction. A notable exception is an important class of membrane-bound O sub(2)-...

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Bibliographic Details
Published in:Energy & environmental science 2014, Vol.7 (4), p.1426-1433
Main Authors: Murphy, Bonnie J, Sargent, Frank, Armstrong, Fraser A
Format: Article
Language:English
Subjects:
Bacteria
Catalysts
Hydrogenase
Intermetallics
Iron compounds
Nickel base alloys
Nickel compounds
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Summary:Many hydrogenases are highly electroactive when attached to an electrode, and most exhibit reversible 2H super(+)/H sub(2) electrocatalysis, i.e.only a minuscule overpotential is required to drive the reaction in either direction. A notable exception is an important class of membrane-bound O sub(2)-tolerant [NiFe] hydrogenases that appear only to catalyse H sub(2) oxidation (the uptake reaction), at a substantial overpotential and with little activity for H sub(2) production, yet possess an active site that is structurally very similar to that of standard, reversible [NiFe] hydrogenases (Volbeda et al., Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 5305-5310). In a discovery providing important insight into this puzzle, we show that the O sub(2)-tolerant [NiFe] hydrogenase (Hyd-1) from E. coli converts into a reversible electrocatalyst as the pH is lowered from 8 to 3 and becomes an efficient H sub(2) producer below pH 4. The transformation to a reversible electrocatalyst is not due, trivially, to the higher substrate (H super(+) sub(aq)) availability at low pH but to a large shift in the enzyme's catalytic bias. Systematic investigations provide compelling evidence that the factor controlling this behaviour is the distal [4Fe-4S] cluster, a spectroscopically elusive site that provides the natural entry point for electrons into the enzyme. In E. coli cells, Hyd-1 is located in the periplasmic (extracytoplasmic) compartment and thus, being exposed to the pH extremes of the gastrointestinal tract or the external environment, is a potential catalyst for H sub(2) production by these bacteria. In a wider context, the observation and proposal are highly relevant for biohydrogen production and catalysis.
ISSN:1754-5692
1754-5706
DOI:10.1039/c3ee43652g