TABLE 2.

Effect of NifX on in vitro synthesis of FeMo-co with purified components^a

NifX added (μg of protein)	DJ42.48 extract (mg of protein)	Activity (nmol of ethylene formed/min)	Fold stimulation
None	None	0.52	1.0
1.9		1.48	2.8
3.8		1.77	3.4
7.5		1.69	3.2
	2.2	1.40	2.7
1.9	2.2	6.52	12.5
3.8	2.2	7.34	14.1
7.5	2.2	8.04	15.5

^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.