Theoretical study of dioxygen induced inhibition of [FeFe]-hydrogenase.

Hydrogenases comprise a variety of enzymes that catalyze the reversible oxidation of molecular hydrogen. Out of this group, [FeFe]-hydrogenase shows the highest activity for hydrogen production which is, therefore, of great interest in the field of renewable energies. Unfortunately, this comes with the flaw of a generally very high sensitivity against molecular oxygen that irreversibly inhibits this enzyme. While many studies have already addressed the mechanism of hydrogen formation by [FeFe]-hydrogenase, little is known about the molecular and mechanistic details leading to enzyme inactivation by O(2). In order to elucidate this process, we performed density functional theory calculations on several possible O(2) adducts of the catalytic center--the so-called H-cluster--and show that the direct interaction of the [2Fe](H) subsite with dioxygen is an exothermic and specific reaction in which O(2) most favorably binds in an end-on manner to the distal Fe(d). Based on the results, we propose a protonation mechanism that can explain the irreversibility of dioxygen-induced enzyme inactivation by water release and degradation of the ligand environment of the H-cluster.