NiFe second electron transfer

Fig. 7. Approximate transition state (structure 8) for the second electron transfer in [NiFe] hydrogenase. The oxidation states are Ni(I-II) and Fe(II). Distances are given in A.

A second approach created a fusion protein from a PSI subunit (PsaE) and a nickel-iron [NiFe] hydrogenase [12], This new protein was then assembled into a PSI mutant lacking the PsaE subunit. The fused enzymatic system was attached to a gold surface in the same way as the PSn electrode described above using a His-tag on PSI, Ni(n) and NTA functionalities on the surface (Fig. 4a, right side). A soluble electron shuttle was used to transfer electrons from the electrode to PSI. From these two approaches the fusion protein is to date the most effective artificial enzymatic system for photo-driven hydrogen production and the activity is comparable to the electrocatalytic activity of the hydrogenase alone immobilized directly on an electrode. 

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