title: Direct assessment of the reduction potential of the [4Fe-4S](1+/0) couple of the Fe protein from Azotobacter vinelandii.
abstract: Recently, it has been demonstrated that the [4Fe-4S] cluster of the Fe protein of nitrogenase from Azotobacter vinelandii can be reduced to an unprecedented all-ferrous state. In this work, the reduction potential for the formation of the all-ferrous state is measured by the reactions of the reduced and oxidized Fe protein with a variety of chemical redox active agents, and by mediated spectroelectrochemical titration. Redox titrations obtain a potential ca. -790 mV/NHE for the formation of the all-ferrous state, a value consistent with the chemical reactivity experiments and with recent theoretical calculations. At present, no known redox protein in A. vinelandii is capable of generating the all-ferrous Fe protein.
authors.affiliation: Department of Molecular Biology and Biochemistry, University of California, Irvine, California 92697-2025, USA.
authors.forename: Maolin
authors.initials: M
authors.lastname: Guo
authors.forename: Filip
authors.initials: F
authors.lastname: Sulc
authors.forename: Markus W
authors.initials: MW
authors.lastname: Ribbe
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Farmer
authors.forename: Barbara K
authors.initials: BK
authors.lastname: Burgess
mesh_terms: D016948:Azotobacter vinelandii / Q000201:enzymology*; D004572:Electrolysis; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010088:Oxidoreductases; C029130:nitrogenase reductase