Voltammetric studies of the reactions of iron-sulphur clusters ([3Fe-4S] or [M3Fe-4S]) formed in Pyrococcus furiosus ferredoxin.
Reactions of the [3Fe-4S] cluster and various metallated [M3Fe-4S] adducts co-ordinated in the ferredoxin from the hyperthermophile Pyrococcus furiosus have been studied by protein-film voltammetry, bulk-solution voltammetry, solution kinetics and magnetic CD (MCD). The [3Fe-4S] cluster exhibits two couples, [3Fe-4S]+/0 and [3Fe-4S]0/2-. Film voltammetry is possible over a wide pH range (2-8), revealing that the [3Fe-4S]+/0 couple shows a complex pH dependence with pKred1=2.8, pKox=4.9 and pKred2=6.7. From MCD, pKred1 corresponds with protonation of [3Fe-4S]0 to give a spectroscopically distinct species, as reported for ferredoxins from Azotobacter and Sulfolobus. The status of the disulphide/disulphydryl entity makes no significant difference to the data (given for the -S-S- form). Formation of the hyper-reduced [3Fe-4S]2- state is observed, requiring 3H+ for the overall 3e- reduction of [3Fe-4S]+, the change therefore being electroneutral. By comparison with the ferredoxin from Desulfovibrio africanus, uptake of Fe(II) and other M(II) by [3Fe-4S]0 to give [M3Fe-4S] clusters is slow (t1/2>10 min at room temperature, slower still if the protein is adsorbed on the electrode), whereas reaction with Tl(I) to produce [Tl3Fe-4S] is very rapid (t1/2<<1 s), suggesting that co-ordination of Tl does not require reorganization of the protein structure. Rates of formation of [3Fe-4S] from [M3Fe-4S] adducts increase sharply at high potentials, showing that metal release involves a labile 'super-oxidized' [M3Fe-4S]3+ state.
Fawcett
S E
SE
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QR, UK.
Davis
D
D
Breton
J L
JL
Thomson
A J
AJ
Armstrong
F A
FA
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods*; D005288:Ferredoxins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry; D007700:Kinetics; D008280:Magnetics; D008670:Metals / Q000378:metabolism / Q000493:pharmacokinetics; D010084:Oxidation-Reduction; D020027:Pyrococcus furiosus / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013057:Spectrum Analysis / Q000379:methods; D013455:Sulfur / Q000737:chemistry; D013816:Thermodynamics
D001426:Bacterial Proteins; D005288:Ferredoxins; D008670:Metals; D013455:Sulfur; D007501:Iron