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 catal ytically active and inactive forms, have been identified and investigated e xperimentally. Until recently, the geometric structure of each form remaine d an open question. Several recent theoretical studies with density functio nal theory have attempted to redress this deficiency. In this commentary, t he similarities and differences among the structures proposed by these stud ies will be addressed.