title: Reactions with the oxidized iron protein of Azotobacter vinelandii nitrogenase: formation of a 2Fe center.
abstract: The Fe-S center of oxidized Fe protein from Azotobacter vinelandii nitrogenase is decomposed by alpha,alpha'-dipyridyl in a biphasic process. In the presence of MgATP, 2 Fe are immediately removed by chelation while the additional irons are removed only after several hours. A slower biphasic Fe release also was observed in the presence of chelator alone. MgADP prevented the Fe release by chelator. An intermediate in the reaction was isolated containing 2 Fe. The visible spectrum of the intermediate was similar to that of 2Fe-2S ferredoxins (epsilon max at 325, 416, and 460 nm of 16.1, 11.3, and 9.0 mM-1 cm-1). The 2Fe form was electron paramagnetic resonance (EPR) silent until partially reduced with sodium dithionite. The EPR spectral properties were similar to 2Fe-2S ferredoxins; namely, the Fe center had resonances at g = 2.00, 1.94, and 1.92 which were detectable, essentially unbroadened at 70 K. The results suggest that in the oxidized (2+) state Fe protein can undergo a 4Fe to 2Fe conversion.
mesh_terms: D015082:2,2'-Dipyridyl / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001395:Azotobacter / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D009591:Nitrogenase / Q000378:metabolism*; D010088:Oxidoreductases; D013053:Spectrophotometry; D013997:Time Factors
chemical_list: D015082:2,2'-Dipyridyl; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase