Journal
JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY
Volume 14, Issue 8, Pages 1275-1288Publisher
SPRINGER
DOI: 10.1007/s00775-009-0572-y
Keywords
Electrochemistry; Hydrogenase; Hyperthermophile; Carbon nanotube; Inhibitors
Funding
- Re gion Provence - Alpes - Cote d'Azur
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The electrochemistry of membrane-bound [NiFe] hydrogenase I ([NiFe]-hase I) from the hyperthermophilic bacterium Aquifex aeolicus was investigated at gold and graphite electrodes. Direct and mediated H-2 oxidation were proved to be efficient in a temperature range of 25-70 A degrees C, describing a potential window for H-2 oxidation similar to that of O-2-tolerant hydrogenases. Search for enhancement of current densities and enzyme stability was achieved by the use of carbon nanotube coatings. We report high catalytic currents for H-2 oxidation up to 1 mA cm(-2), 10 times higher than at the bare electrode. Interestingly, high stability of the direct catalytic process was observed when encapsulating A. aeolicus [NiFe]-hase I into a carboxylic functionalized single walled carbon nanotube network. This suggests a peculiar interaction between the enzyme and the electrode material. The parameters that governed the orientation of the enzyme before electron transfer were thus investigated using self-assembled-monolayer gold electrodes. No control of the orientation by the charge or the hydrophobicity of the interface was demonstrated. This behavior was explained on the basis of a structural comparison between A. aeolicus [NiFe]-hase I and Desulfovibrio fructosovorans [NiFe] hydrogenase, which revealed the absence of acidic residues and an additional loop in the environment of the [4Fe-4S] distal cluster in A. aeolicus [NiFe]-hase I. Finally, the effect of inhibitors on the direct oxidation of H-2 by A. aeolicus [NiFe]-hase I encapsulated in a single walled carbon nanotube network was investigated. No inhibition by CO and tolerance toward O-2 were observed. Discussion of the reasons for such tolerance was undertaken on the basis of structural comparison with hydrogenases from aerobic bacteria.
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