Hydrogenases, hydrogen-splitting enzymes, are of common interest, because they may substitute platinum as a catalyst for the splitting of hydrogen. [Fe]-hydrogenase is a new type of hydrogenase without a crystal structure available as yet. In this work the crystal structures of [Fe]-hydrogenase apoenzyme, holoenzyme and cyanide-inhibited holoenzyme are presented. [Fe]-hydrogenase is a mononuclear iron enzyme containing a new biological cofactor (FeGP cofactor). The iron in [Fe]-hydrogenase is pentacoordinated (one sulfur, one nitrogen, two CO and one unknown ligand, that can be substituted by cyanide).
