Table 1.

Mobilization of molybdenum from NifQ under conditions of FeMo-co synthesis

Protein	Molybdenum, mol
NifQ
Before incubation (as isolated)	0.36 ± 0.03
After incubation with NifEN	0.28 ± 0.02
After incubation with NifH	0.29 ± 0.01
After incubation with NifEN and NifH	0.11 ± 0.01
After incubation with NifEN, NifH and apo-NifDK	0.15 ± 0.02
NifEN
Before incubation (as isolated)	0.24 ± 0.03
After incubation with NifQ	0.19 ± 0.02
After incubation with NifQ and NifH	0.45 ± 0.06
NifH
Before incubation (as isolated)	0.009 ± 0.002
After incubation with NifQ	0.013 ± 0.001
After incubation with NifQ and NifEN	0.060 ± 0.010

Purified as-isolated NifQ was incubated with purified (i) NifH, (ii) NifEN, (iii) NifH and NifEN, or (iv) NifH, NifEN and apo-NifDK in reaction mixtures that also contained Mg-ATP, DTH, and homocitrate. No external source of molybdenum was added to the mixtures. NifQ, NifH, and NifEN proteins were reisolated by chromatography after incubation. Molybdenum content was quantified by ICP-OES and is shown in mol of molybdenum per mol of protein (i.e. NifQ monomer, NifH dimer, or NifEN tetramer). Values are the average of at least two independent determinations ± SD.