Table 2. Subunit compositions, metal contents, and S = 1/2 EPR signal features.

		Metal content			S = 1/2 EPR signal
Protein	Subunit composition	Fe, mol metal/mol protein	Mo,* mol metal/mol protein	V,* mol metal/mol protein	g values			Spin integration, mol spin/mol αβ-dimer
ΔnifB Av1	α2β2†	15.4 ± 0.8	<0.01	<0.01	None
ΔnifH Av1	α2β2†	15.5 ± 0.9	<0.01	<0.01	2.06	1.92	1.89	0.4 ± 0.1
ΔnifH Av1′	α2β2†	15.4 ± 0.4	<0.01	<0.01	2.06	1.92	1.89	1.1 ± 0.2
ΔnifB Av1v	αβ2‡	8.5 ± 0.4	<0.01	<0.01	2.08	1.92	1.89	0.9 ± 0.1

^*WT Av1 and WT Av1^v protein standards show metal contents of 2.0 ± 0.1 Mo and 1.8 ± 0.2 V, respectively.

^†The α- and β-subunits are encoded by nifD and nifK, respectively. Determination of the subunit composition of the protein is based on quantitative analysis of the SDS/PAGE (Fig. 1A) and the elution profiles on the Sephacryl S-200 HR gel filtration column (data not shown).

^‡The α- and β-subunits are encoded by vnfD and vnfK, respectively. Determination of the subunit composition of the protein is based on quantitative analysis of the SDS/PAGE (Fig. 1A), quantitative analysis of the N-terminal amino acid sequence (data not shown), and the elution profiles on the Sephacryl S-200 HR gel filtration column (data not shown).