title: Electron transfer in nitrogenase catalysis.
abstract: Nitrogenase is a two-component enzyme that catalyzes the nucleotide-dependent reduction of N2 to 2NH3. This process involves three redox-active metal-containing cofactors including a [4Fe-4S] cluster, an eight-iron P cluster and a seven-iron plus molybdenum FeMo-cofactor, the site of substrate reduction. A deficit-spending model for electron transfer has recently been proposed that incorporates protein conformational gating that favors uni-directional electron transfer among the metalloclusters for the activation of the substrate-binding site. Also reviewed is a proposal that each of the metal clusters cycles through only two redox states of the metal-sulfur core as the system accumulates the multiple electrons required for substrate binding and reduction. In particular, it was suggested that as FeMo-cofactor acquires the four electrons necessary for optimal binding of N2, each successive pair of electrons is stored as an Fe-H--Fe bridging hydride, with the FeMo-cofactor metal-ion core retaining its resting redox state. We here broaden the discussion of stable intermediates that might form when FeMo-cofactor receives an odd number of electrons.
authors.affiliation: Department of Chemistry and Biochemistry, Utah State University, 0300 Old Main Hill, Logan, UT 84322, USA. lance.seefeldt@usu.edu
authors.forename: Lance C
authors.initials: LC
authors.lastname: Seefeldt
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
authors.forename: Dennis R
authors.initials: DR
authors.lastname: Dean
mesh_terms: D055162:Biocatalysis; D004579:Electron Transport; D009591:Nitrogenase / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D013379:Substrate Specificity
chemical_list: D009591:Nitrogenase