Nickel–Iron Hydrogenases

Abstract

Ni–Fe hydrogenases catalyze the cleavage or the production of the most simple of chemical compounds, molecular hydrogen. This review provides an overview of the literature on these enzymes that has been published before the year 2000. On the basis of atomic models plausible pathways of substrates and products are described, including a hydrophobic tunnel network for H 2 diffusion, a suitable arrangement of three iron–sulfur clusters for electron transfer, a network of buried water molecules, and a magnesium site that could be involved in proton transfer. A combination of protein crystallography, electron paramagnetic resonance, and Fourier transform infrared spectroscopic studies has allowed the elucidation of the unique architecture of the active site. This consists of a thiolate‐coordinated Ni–Fe unit involving one carbon monoxide and two cyanide ligands to the iron, leaving two metal coordination sites available for substrate binding. Understanding the catalytic mechanism of these fascinating enzymes might be helpful for the development of cheap catalysts for fuel cells working on H 2 or of cheaper production methods for this clean fuel.

Detoxification of superoxide without production of H 2 O 2 : Antioxidant activity of superoxide reductase complexed with ferrocyanide

“…Addition of ferrocyanide as a cofactor to SOR provides a new detoxification mechanism for superoxide that may have a biological relevance. Although synthesis of ferrocyanide in cells has not been investigated to date, the presence of cyanide as a metal ligand has been well characterized in hydrogenases (15). Interestingly, hydrogenases are usually found in the same type of bacteria where SORs are naturally expressed and these cells possess enzymatic systems that can synthesize CN Ϫ , HypE and HypF (16), and incorporate it into proteins.…”

Analysis of the transcarbamoylation‐dehydration reaction catalyzed by the hydrogenase maturation proteins HypF and HypE

“…Escherichia coli possesses four hydrogenases (Hyd1–Hyd4) which are all members of the NiFe class [1,2]. In these enzymes, the bimetallic active centre is hooked to the protein via four cysteine thiolates whereby two of them act as ligands bridging the iron and the nickel (for a review, see [3]). The most intriguing feature, however, is that the iron carries three diatomic, nonprotein ligands which in the classical case consist of two cyanides and one carbon monoxide [4,5].…”

A QM/MM study of proton transport pathways in a [NiFe] hydrogenase

“…There has been much speculation about the routes of proton transfer in [NiFe] hydrogenases 19, 22. Based on extensive geometrical analyses of networks of protonatable groups in the crystallographic structures, using both visual inspection and calculation, two basic pathways appear possible.…”

“…The second pathway (Fig. 2) goes through the C‐terminal His‐549(Q) to Glu‐53(Q) and then onto waters, lying close to the surface, that surround a nearby Mg 2+ cation 19, 22. This second pathway is around 27 Å long and entails not less than 10 proton‐transfer steps.…”