Table 2. Determination of factors required for FeMoco maturation.

	Activities*
Assay condition	C2H4 formation under C2H2/Ar	H2 formation under Ar	NH3 formation under N2	H2 formation under N2
Complete†	191 ± 26 (100)	316 ± 11 (100)	96 ± 6 (100)	65 ± 13 (100)
Complete plus (NH4)2MoS4‡	0 (0)	2 ± 0.04 (<1)	0 (0)	2 ± 0.2 (3)
Complete minus MgATP	0 (0)	0 (0)	0 (0)	0 (0)
Complete minus Fe protein	0 (0)	0 (0)	0 (0)	0 (0)
Complete minus homocitrate	0 (0)	0 (0)	0 (0)	0 (0)
Complete minus molybdate§	10 ± 1 (5)	15 ± 3 (5)	0 (0)	0 (0)
Complete minus NifEN	0 (0)	0 (0)	0 (0)	0 (0)
Complete minus ΔnifB MoFe protein	0 (0)	0 (0)	0 (0)	0 (0)
Complete minus NifEN, plus ΔnifB NifEN¶	0 (0)	1 ± 0.1 (<1)	0 (0)	0 (0)
ΔnifB MoFe protein alone	0 (0)	0 (0)	0 (0)	0 (0)
NifEN alone	0 (0)	0 (0)	0 (0)	0 (0)
ΔnifB NifEN alone	0 (0)	1 ± 0.1 (<1)	0 (0)	0 (0)

Data are expressed as nmol per min per mg of protein. Percentages are given in parentheses.

^*The lower detection limits were 0.01, 0.02, 0.001, and 0.02 nmol per min per mg of protein for C₂H₄ formation under C₂H₂/Ar, H₂ formation under Ar, NH₃ formation under N₂, and H₂ formation under N₂, respectively

^†The complete assay contains purified NifEN, purified ΔnifB MoFe protein, purified Fe protein, molybdate, homocitrate, and MgATP at concentrations described in Materials and Methods

^‡Insertion of FeMoco into ΔnifB MoFe protein was inhibited by the addition of (NH₄)₂MoS₄ at the beginning of the experiment, as described in Materials and Methods

^§The minor activities were likely caused by molybdenum contamination in the assays

^¶Assay contained the same components as described in †, except that NifEN was replaced by equimolar amounts of ΔnifB NifEN