Fig. 3. The di-iron centre in Dd Bfr, showing the residues coordinating as terminal or bridging ligands. Red dashed lines indicate bonds, while black dashed lines indicate distances >2.60 Å. The distance between the iron atoms in the as ‘isolated’ structure is 3.71 Å (PDB 1nfv), while in the reduced structure it is 3.99 Å (PDB 1nf4). (A) View of the centre in the ‘as isolated’ structure with the unequivocally identified ligands. (B) View of the site in the ‘cycled’ oxidized structure (PDB 1nf6). Fe1 is strongly depleted in this structure with an occupancy between 0 and 30% in the various crystallographic independent subunits.