Recent theoretical predictions of the active site for the observed forms in the catalytic cycle of Ni-Fe hydrogenase

Various states or forms of the active site in Ni-Fe hydrogenase, both catalytically active and inactive forms, have been identified and investigated experimentally. Until recently, the geometric structure of each form remained an open question. Several recent theoretical studies with density functional theory have attempted to redress this deficiency. In this commentary, the similarities and differences among the structures proposed by these studies will be addressed.