Sulfoxygenation of Active Site Models of [NiFe] and [FeFe] Hydrogenases - A Commentary on Possible Chemical Models of Hydrogenase Enzyme Oxygen Sensitivity
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The organometallic active sites in [NiFe]- and [FeFe]H2ases are sensitive to oxygen in varying degrees. The microorganisms that utilize these enzymes for their hydrogen metabolism, and the enzymes themselves, have evolved from a reducing to an oxidizing environment in ways to avoid competition with oxygen, primarily by burying the active site machinery deeply within the protein matrix. In the case of [Ni-Fe]H2ase, biological studies indicate that repair mechanisms exist for reversible O2-inhibition processes. This Microreview explores the possibility that S-oxygenation may represent reparable O-damaged enzyme active sites. Such S-oxygenation has precedent in chemical models for the terminal thiolate sulfur atoms of the nickel site in [NiFe]H2ase as well as the bridging thiolate sulfur in the [FeFe]H2ase active site. A discussion of the processes of O 2 damage leading to both reversible and irreversible enzyme inhibition, and reclamation of activity in the H2ases, as explored by various biochemical assays and spectroscopic methods, is also presented. 2011 Wiley-VCH Verlag GmbH & Co. KGaA.