Table 1.

Specific substrate-reducing activities of substrate-free DPOR, apo nitrogenase variant, and holo nitrogenase

Enzyme	Activities (nmol⋅min−1⋅mg−1)
	Chlide formation from 0.02 mM Pchlide	NH3 formation from 40 mM N3−	NH3 formation from 40 mM N2H4	NH3 formation from 100% N2	C2H4 formation from 60% C2H2	C2H4 formation from 100% CO
Substrate-free DPOR	1.1 ± 0.1	1.2 ± 0.1	1.07 ± 0.01	0 (0)	0 (0)	0 (0)
Apo nitrogenase variant	0 (0)	2.4 ± 0.3	0.4 ± 0.2	0 (0)	3.3 ± 0.5	0 (0)
Holo nitrogenase	0 (0)	624 ± 16	263 ± 2	481 ± 19	2216 ± 145	0.013 ± 0.001

Specific substrate-reducing activities of substrate-free DPOR, apo nitrogenase variant, and holo nitrogenase are shown. Substrate-free DPOR consists of L₂ and (NB)₂, whereas apo nitrogenase variant consists of NifH₂ and apo (NifDK)₂ variant. Data are presented as mean ± SD (n = 4). The lower detection limits were 0.08, 0.0005, and 0.001 nmol⋅min⁻¹⋅mg⁻¹ of protein for Chlide-, C₂H₄-, and NH₃-formation, respectively.