Dithionite-dependency of precursor maturation on NifEN. NifENPrecursor was first converted to NifEN“FeMoco” in varying concentrations of dithionite (0, 2, 10, 20 and 40 mM, respectively) and, subsequently, NifEN“FeMoco” was re-isolated and used as a FeMoco source for the reconstitution of FeMoco-deficient ΔnifB MoFe protein. Shown are the specific C2H2-reducing activities of MoFe protein upon reconstitution with NifEN“FeMoco” prepared at different dithionite concentrations. The calculated
solution potentials9 are indicated.