Table 3. Effect of Fe protein variants and various nucleotides on FeMoco maturation.

Factors	Activities*
Fe protein
No Fe protein	0 (0)
WT Fe protein	196 ± 6 (100)
A157S Fe protein†‡	18 ± 4 (9)
A157G Fe protein†§	11 ± 1 (6)
M156C Fe protein†¶	6 ± 2 (3)
Nucleotide∥
No nucleotide	0 (0)
ATP	186 ± 10 (100)
ADP**	0 (0)
ATPγS**	0 (0)
AMPPNP**	0 (0)

Data are expressed as nmol of C₂H₄ evolution per min per mg of protein. Percentages are given in parentheses. ATPγS, adenosine 5′-O-(3-thiotriphosphate; AMPPNP, 5′-adenylylimidodiphosphate.

^*The lower detection limit was 0.01 nmol of C₂H₄ evolution per min per mg of protein

^†All Fe protein variants are able to bind MgATP (27–29)

^‡A157S Fe protein is unable to undergo a MgATP-induced conformational change and does not support MgATP hydrolysis (27)

^§A157G Fe protein undergoes a delayed conformational change upon MgATP binding, resulting in a reduced substrate-reduction activity (28)

^¶M156C Fe protein undergoes a MgATP-induced conformational change that differs from WT Fe protein, resulting in the loss of substrate-reduction activity (29)

^∥Identical results have been obtained by using 10-, 50-, and 100-fold molar excess of nucleotides relative to Fe protein in the FeMoco-maturation assay

^**Note that, with the addition of excess MgATP as described in Materials and Methods, these nucleotides do not inhibit substrate-reduction activity of the WT MoFe protein