Table S1.

The redox potential of ferredoxins is not the primary factor limiting electron transfer to nitrogenase from pyruvate–ferredoxin (flavodoxin) oxidoreductase (NifJ)

Organism*	Location	Genes	Redox potential†	Relative nitrogenase activity, % acetylene reduction‡
				FeFe	MoFe
Ko	—	nifF	−412 mV (34)	100 ± 6	100 ± 15
	—	ΔnifF	—	31 ± 6	10 ± 3
As	Heterocyst	fdxH	−351 mV (46)	153 ± 21	100 ± 6
	Vegetative	petF	−384 mV (46)	110 ± 14	81 ± 11
Cr	Chloroplast	PETF	−398 mV (47)	105 ± 11	90 ± 5
	Chloroplast	FDX2	−321 mV (47)	92 ± 4	87 ± 4
Zm	Chloroplast	FDI	−423 mV (48)	96 ± 9	56 ± 6
	Chloroplast	FDII	−406 mV (48)	75 ± 7	50 ± 7
	Root plastid	FDIII	−321 mV (49)	82 ± 9	51 ± 7
At	Chloroplast	FD1	−425 mV (50)	59 ± 6	36 ± 6
	Chloroplast	FD2	−433 mV (50)	76 ± 11	50 ± 11
	Root plastid	FD3	−337 mV (50)	68 ± 4	34 ± 8

^*Origin of flavodoxin or ferredoxin genes expressed in E. coli.

^†Redox potentials reported previously with references in parentheses.

^‡Nitrogenase activity of E. coli strains expressing NifJ in the presence of the indicated flavodoxin or ferredoxin components. Activities observed from the minimal FeFe or reassembled MoFe nitrogenase systems in the presence of the NifJ–NifF module represent 100% activity, respectively. Data presented are mean values based on at least three independent experiments.