Fe-only Hydrogenase
- Page ID
- 399
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Hydrogenase enzymes catalyze the reversible oxidation of molecular hydrogen to protons and electrons [H2 ↔ 2H+ + 2e-] [1].The two most studied classes are Ni-Fe hydrogenases and Fe-only hydrogenases. In general, Ni-Fe hydrogenase enzymes consume molecular hydrogen as a fuel source, and Fe-only hydrogense enzymes produce molecular hydrogen [2].
Representation of Fe-only Hydrogenase
Crystal structure of the hydrogenase was obtained from a sulfate-reducing microorganism to 1.6 Å resolution (fig 1). Desulfovibrio desulfuricans (DdH) is a 53 kDa protein located in the periplasm [3]. Crystal structure of the enzyme was obtained from Clostridium pasteurianum an anaerobic soil microorganism to 1.8 Å resolution (fig 2). This enzyme, CpI, is a 61 kDa protein found in the cytoplasm [4]. DdH is a dimer with three 4Fe-4S cubanes and a H-cluster (fig 3)[5]. CpI is a monomer with three 4Fe-4S cubanes, one 2Fe-2S cluster, and a H-cluster (fig 4)[5].
Point group symmetry
Electronic Structure of the 2Fe Subunit
Reactivity of Fe only hydrogenase
When enzyme is isolated in air it changes its state from Fe(II)-Fe(I)(OH) to Fe(II)-Fe(I)(vacant). Actually, an exchangeable water molecule is bound to the active site labeled “vacant” in the figure. The enzyme then accepts an electron and a proton so that Fe(II)-Fe(I) is oxidized to protonated Fe(I)-Fe(I) Complex.The enzyme changes configuration, and a hydride is transferred into the active site of Fe(II) by reduction. The subsequent addition of an electron and a proton allows for the formation of molecular hydrogen, and the loss of H2 returns the system back to its native active form [6].
