TABLE 3.

Effect of partially purified unknown component on in vitro synthesis of FeMo-co with purified components plus NifX^a

NifX added (μg of protein)	Partially purified unknown component (mg of protein)	Activity (nmol of ethylene formed/min)	Fold stimulation
None	None	0.55	1.0
2.1		1.60	2.9
4.2		1.79	3.2
	0.21	1.56	2.8
	0.42	1.90	3.4
2.1	0.21	4.18	7.6
2.1	0.42	7.54	13.7
2.1	0.64	10.42	18.9
2.1	0.85	12.55	22.8

^aThe reaction mixture contained 100 nmol of homocitrate, 10 nmol of molybdate, 200 μl of ATP-dithionite solution, NifB-co (1 nmol of Fe), apodinitrogenase (12 μg of protein), NifNE (3 μg of protein), and dinitrogenase reductase (52 μg of protein) in a final volume of 550 μl. Twelve micrograms of apodinitrogenase gave 15.5 nmol of ethylene formed/min when assayed with excess purified FeMo-co, 3 μg of NifNE gave 13.2 nmol of ethylene/min when assayed with an extract of strain DJ35 (ΔnifE), NifB-co (1 nmol of Fe) gave 25.4 nmol of ethylene/min when assayed with an extract of strain UW45 (nifB mutant), and 52 μg of dinitrogenase reductase gave 82.4 nmol of ethylene/min when assayed with purified dinitrogenase, as described in Materials and Methods.