Electron-paramagnetic-resonance studies on the redox properties of the molybdenum-iron protein of nitrogenase between +50 and −450 mV

The midpoint potentials, Em, for the oxidation of the characteristic e.p.r. signal with g values near 4.3, 3.7 and 2.01, of the nitrogenase Mo-Fe proteins from a number of bacteria were measured. They were 0mV for Clostridium pasteurianum, -42mV for Azotobacter chroococcum and Azotobacter vinelandii, -95mV for Bacillus polymyxa and -180mV for Klebsiella pneumoniae Mo-Fe proteins at pH 7.9. The oxidations were thermodynamically reversible for …