title: Isolation and characterization of an Fe,-S8 ferredoxin (ferredoxin II) from Clostridium thermoaceticum.
abstract: A second ferredoxin protein was isolated from the thermophilic anaerobic bacterium Clostridium thermoaceticum and termed ferredoxin II. This ferredoxin was found to contain 7.9 +/- 0.3 iron atoms and 7.4 +/- 0.4 acid-labile sulfur atoms per mol of protein. Extrusion studies of the iron-sulfur centers showed the presence of two [Fe4-S4] centers per mol of protein and accounted for all of the iron present. The absorption spectrum was characterized by maxima at 390 nm (epsilon 390 = 30,400 M-1cm-1) and 280 nm (epsilon 280 = 41.400 M-1 cm-1) and by a shoulder at 300 nm. The ration of the absorbance of the pure protein at 390 nm to the absorbance at 280 nm was 0.74. Electron paramagnetic resonance data showed a weak signal in the oxidized state, and the reduced ferredoxin exhibited a spectrum typical of [Fe4-S4] clusters. Double integration of the reduced spectra showed that two electrons were necessary for the complete reduction of ferredoxin II. Amino histidine, and 1 arginine, and a molecular weight of 6,748 for the native protein. The ferredoxin is stable under anaerobic conditions for 60 min at 70 degrees C. The average oxidation-reduction potential for the two [Fe4-S4] centers was measured as -365 mV.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D003013:Clostridium / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins / Q000302:isolation & purification*; D007501:Iron / Q000032:analysis; D008970:Molecular Weight; D010084:Oxidation-Reduction; D013053:Spectrophotometry; D013455:Sulfur / Q000032:analysis
chemical_list: D000596:Amino Acids; D005288:Ferredoxins; D013455:Sulfur; D007501:Iron