title: Electrochemical and spectroscopic characterization of the 7Fe form of ferredoxin III from Desulfovibrio africanus.
abstract: Desulfovibrio africanus ferredoxin III is a monomeric protein (Mr 6585) containing seven cysteine residues and 7-8 iron atoms and 6-8 atoms of acid-labile sulphur. It is shown that reversible unmediated electrochemistry of the two iron-sulphur clusters can be obtained by using a pyrolytic-graphite-'edge' carbon electrode in the presence of an appropriate aminoglycoside, neomycin or tobramycin, as promoter. Cyclic voltammetry reveals two well-defined reversible waves with E0' = -140 +/- 10 mV and -410 +/- 5 mV (standard hydrogen electrode) at 2 degrees C. Bulk reduction confirms that each of these corresponds to a one-electron process. Low-temperature e.p.r. and magnetic-c.d. spectroscopy identify the higher-potential redox couple with a cluster of core [3Fe-4S]1+.0 and the lower with a [4Fe-4S]2+.1+ centre. The low-temperature magnetic-c.d. spectra and magnetization properties of the three-iron cluster show that it is essentially identical with that in Desulfovibrio gigas ferredoxin II. We assign cysteine-11, -17 and -51 as ligands of the [3Fe-4S] core and cysteine-21, -41, -44 and -47 to the [4Fe-4S] centre.
authors.affiliation: Inorganic Chemistry Laboratory, University of Oxford, U.K.
authors.forename: F A
authors.initials: FA
authors.lastname: Armstrong
authors.forename: S J
authors.initials: SJ
authors.lastname: George
authors.forename: R
authors.initials: R
authors.lastname: Cammack
authors.forename: E C
authors.initials: EC
authors.lastname: Hatchikian
authors.forename: A J
authors.initials: AJ
authors.lastname: Thomson
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003901:Desulfovibrio / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins; D006863:Hydrogen-Ion Concentration; D007501:Iron; D008280:Magnetics; D008969:Molecular Sequence Data; D009355:Neomycin; D010084:Oxidation-Reduction; D013057:Spectrum Analysis; D014031:Tobramycin
chemical_list: D005288:Ferredoxins; D007501:Iron; D009355:Neomycin; D014031:Tobramycin