Isocyanides inhibit [Fe]-hydrogenase with very high affinity

Fe]-Hydrogenase catalyzes the reversible activation of H₂. CO and CN⁻ inhibit this enzyme with low affinity (K_i ≅ 0.1 mM) by binding to the iron site of the bound iron-guanyrylpyridinol cofactor. We report here that isocyanides, which are formally isoelectronic with CO and CN⁻, strongly inhibit Fe]-hydrogenase (K_i as low as 1 nM). The NiFe]- and FeFe]-hydrogenases tested were not inhibited by isocyanides. UV–Vis and infrared spectra revealed that the isocyanides bind to the iron center of Fe]-hydrogenase. The inhibition kinetics are in agreement with the proposed catalytic mechanism, including the open/closed conformational change of the enzyme.