A modified flavodoxin with altered redox potentials is less efficient in electron transfer to nitrogenase

The flavodoxins of the Azotobacter vinelandii wild-type and a mutant strain TZN 200 have been studied. Although the primary structure of the two proteins is the same, the ability of the mutant flavodoxin to donate electrons to nitrogenase is reduced by 75%. One reason may be the raised mid-point potential of −435 mV for the semiquinone/hydroquinone couple in the mutant flavodoxin. The respective redox potential for the wild-type flavodoxin was found to be −480 mV. As shown by paper chromatography and light absorption spectroscopy, the structure of FMN is modified in the TZN 200 flavodoxin.