Table 1. MoFe protein activity supported by yNifHmit and yNifHcyt purified preparations.

Fe protein	Other co-expressed Nif proteins	C2H2 reduction activity*	N2 fixation activity†	Fe protein to MoFe protein molar ratio
Mitochondrial
yNifHmit	NifM	404±62	ND	20
yNifHmit	NifM	1,600‡,§	826±60	200
yNifHmit	None	<0.01	ND	≥400
yNifHmit||	NifM, NifU, NifS	430±45§	511±10	30
Cytosolic
yNifHcyt (air)	NifM	<0.01	ND	≥400
yNifHcyt (air)	NifM, NifU, NifS	<0.01	ND	≥400
yNifHcyt (N2)	NifM	102±2	ND	≥400
yNifHcyt (N2)	NifM, NifU, NifS	404±20	ND	30
NifH¶		1,652±23	849±25	40

ND, not determined.

^*Defined as nmol of C₂H₄ formed· per minute per milligram MoFe protein (mean±s.d., n=3).

^†Defined as nmol of NH₃ formed·per minute per milligram MoFe protein (mean±s.d., n=2).

^‡Single determination.

^§See activity titrations in Supplementary Fig. 3.

^||Purified from GF8 cells.

^¶Purified from A. vinelandii.