Immobilization of the [FeFe]-hydrogenase CrHydA1 on a gold electrode: design of a catalytic surface for the production of molecular hydrogen.

Hydrogenase-modified electrodes are a promising catalytic surface for the electrolysis of water with an overpotential close to zero. The [FeFe]-hydrogenase CrHydA1 from the photosynthetic green alga Chlamydomonas reinhardtii is the smallest [FeFe]-hydrogenase known and exhibits an extraordinary high hydrogen evolution activity. For the first time, we immobilized CrHydA1 on a gold surface which was modified by different carboxy-terminated self-assembled monolayers. The immobilization was in situ monitored by surface-enhanced infrared spectroscopy. In the presence of the electron mediator methyl viologen the electron transfer from the electrode to the hydrogenase was detected by cyclic voltammetry. The hydrogen evolution potential (-290 mV vs NHE, pH 6.8) of this protein modified electrode is close to the value for bare platinum (-270 mV vs NHE). The surface coverage by CrHydA1 was determined to 2.25 ng mm(-2) by surface plasmon resonance, which is consistent with the formation of a protein monolayer. Hydrogen evolution was quantified by gas chromatography and the specific hydrogen evolution activity of surface-bound CrHydA1 was calculated to 1.3 micromol H(2)min(-1)mg(-1) (or 85 mol H(2)min(-1)mol(-1)). In conclusion, a viable hydrogen-evolving surface was developed that may be employed in combination with immobilized photosystems to provide a platform for hydrogen production from water and solar energy with enzymes as catalysts.