Alignment of α subunits of nitrogenase isozymes. Shown is an alignment of α subunits of Mo-nitrogenase (PDB ID: 3U7Q), V-nitrogenase (PDB ID: 5N6Y), and Fe-nitrogenase (sequence threaded on to V-nitrogenase PDB ID: 5N6Y using Swiss-Model) highlighting amino acid residues in the cofactor environment. The starting perspective is looking down on the Fe2, 3, 6, 7 face of FeMoco and FeVco. S is in yellow, Fe in orange, Mo in magenta, and V in pink with the homocitrate to the right in grey. Side chains that are 100% conserved among the isozymes are shown in green, whereas side chains where there is variation in the residue in at least one isozyme are shown in red. The residue numbering refers to Mo-nitrogenase. ChimeraX version 1.0 file.