Carbon monoxide as intrinsic ligand to iron in the active site of [fe]-hydrogenase.

Abstract

Structural and spectroscopic studies on [Fe]-hydrogenase revealed an active site mononuclear low spin iron coordinated by the Cys176 sulfur, two CO, and the sp(2) hybridized nitrogen of a 2-pyridinol compound with back bonding properties similar to those of cyanide. Thus, [Fe]-hydrogenases are endowed with an iron-ligation pattern related to that found in the active site of [NiFe]- and [FeFe]-hydrogenases although the three hydrogenases and the enzymes involved in their posttranslational maturation have evolved independently and although CO and cyanide ligands are not found in any other metallo-enzymes. Obviously, low-spin iron complexed with thiolate(s), CO, and cyanide or a cyanide functional analogue plays an essential role in H(2) activation.