title: Azotobacter chroococcum 7Fe ferredoxin. Two pH-dependent forms of the reduced 3Fe clusters and its conversion to a 4Fe cluster.
abstract: Ferredoxin from Azotobacter chroococcum has been studied by low-temperature magnetic-circular-dichroism and electron-paramagnetic-resonance spectroscopy. When aerobically isolated ferredoxin contains a [3Fe-4S] and [4Fe-4S] cluster. Anaerobic treatment with dithionite in the presence of ethanediol reduces the [3Fe-4S] cluster to give two spectroscopically distinct forms RI and RII which are reversibly interconvertible with a pKa approximately 7.5. The higher-pH form, RII, has a high affinity for ferrous ion and converts readily to a [4Fe-4S]1+ cluster, scavenging iron from the medium. The presence of the iron chelator EDTA inhibits this conversion.
mesh_terms: D001395:Azotobacter / Q000032:analysis*; D055598:Chemical Phenomena; D002621:Chemistry; D002942:Circular Dichroism; D004227:Dithionite; D004492:Edetic Acid; D004578:Electron Spin Resonance Spectroscopy; D005288:Ferredoxins; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000032:analysis*; D013696:Temperature
chemical_list: D005288:Ferredoxins; D004227:Dithionite; D004492:Edetic Acid; D007501:Iron