H 2 Conversion in the Presence of O 2 as Performed by the Membrane‐Bound [NiFe]‐Hydrogenase of Ralstonia eutropha

[NiFe]‐hydrogenases catalyze the oxidation of H 2 to protons and electrons. This reversible reaction is based on a complex interplay of metal cofactors including the Ni–Fe active site and several [Fe–S] clusters. H 2 catalysis of most [NiFe]‐hydrogenases is sensitive to dioxygen. However, some bacteria contain hydrogenases that activate H 2 even in the presence of O 2 . There is now compelling evidence that O 2 affects hydrogenase on three levels: 1) H 2 catalysis, 2) hydrogenase maturation, and 3) H 2 ‐mediated signal transduction. Herein, we summarize the genetic, biochemical, electrochemical, and spectroscopic properties related to the O 2 tolerance of hydrogenases resident in the facultative chemolithoautotroph Ralstonia eutropha H16. A focus is given to the membrane‐bound [NiFe]‐hydogenase, which currently represents the best‐characterized member of O 2 ‐tolerant hydrogenases.