title: Isolation, characterization, and biological activity of the Methanococcus thermolithotrophicus ferredoxin.
abstract: A ferredoxin has been isolated from the thermophilic methanogen Methanococcus thermolithotrophicus. The native protein was a monomer exhibiting a molecular weight of 7,262, calculated from the amino acid composition. Its absorption spectrum had two maxima at 390 and 283 nm, with an absorbance ratio A390/A283 of 0.79. The absorption at 390 nm (E = 29 mM-1 cm-1) and the content of iron of the protein are in agreement with the presence of two 4Fe-4S clusters in M. thermolithotrophicus ferredoxin. Its amino acid composition showed the presence of eight cysteine residues, which is the required number of cysteines for the binding of two 4Fe-4S clusters. The protein was characterized by the lack of histidine, arginine, and leucine and a high content of valine. It was unusually stable to high temperatures but not to oxygen. The ESR spectrum of the protein in the oxidized state showed a minor signal at g = 2.01, corresponding to an oxidized 3Fe-4S cluster. The protein, which was difficult to reduce with dithionite or reduced mediators, exhibited in its reduced state a spectrum typical of two interacting reduced 4Fe-4S clusters. M. thermolithotrophicus ferredoxin functioned as an electron acceptor for the CO dehydrogenase complex with an extract free of ferredoxin. No reaction was detected with F420 or hydrogenase.
authors.affiliation: Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, Marseille, France.
authors.forename: E C
authors.initials: EC
authors.lastname: Hatchikian
authors.forename: M L
authors.initials: ML
authors.lastname: Fardeau
authors.forename: M
authors.initials: M
authors.lastname: Bruschi
authors.forename: J P
authors.initials: JP
authors.lastname: Belaich
authors.forename: A
authors.initials: A
authors.lastname: Chapman
authors.forename: R
authors.initials: R
authors.lastname: Cammack
mesh_terms: D000596:Amino Acids / Q000032:analysis; D004578:Electron Spin Resonance Spectroscopy; D019605:Euryarchaeota / Q000032:analysis* / Q000502:physiology; D005288:Ferredoxins / Q000302:isolation & purification* / Q000502:physiology; D006358:Hot Temperature; D007501:Iron / Q000032:analysis; D008795:Metronidazole / Q000378:metabolism; D008970:Molecular Weight; D010084:Oxidation-Reduction; D010100:Oxygen / Q000633:toxicity; D013057:Spectrum Analysis; D013455:Sulfur / Q000032:analysis
chemical_list: D000596:Amino Acids; D005288:Ferredoxins; D008795:Metronidazole; D013455:Sulfur; D007501:Iron; D010100:Oxygen