Fig. 2.

Cyclic voltammetry profiles of [FeFe]-hydrogenases, CpI (A) and CrHydA1 (B), on PGE electrodes and equilibrated with 100% H₂ flowing in the headspace (red trace): the trace shows that, depending upon the potential applied, both H₂ oxidation and H⁺ reduction are carried out by the enzyme. When CO is injected, the enzymes are unable to carry out H₂ oxidation, and H⁺ reduction begins at a more negative potential (below −0.6 V vs. SHE) where CO is released (blue trace). Conditions: pH 7.0 (0.10 M phosphate buffer); temperature, 0 °C; scan rate, 20 mV⋅s⁻¹.