The iron protein of nitrogenase is responsible for electron transfer and for controlling the redox potential.
When a Mg-ATP unit docks on the protein, its reduction potential is lowered by ca. 100 mV. This step is a prerequisite for electron transfer to the Mo-Fe protein, where nitrogen is reduced.
Attachment of the iron-sulfur cluster to the protein (a typical Fe4S4 cluster with 4 cysteine residues and 4 sulfido ligands)
Binding pocket for ADP