Desulfoferrodoxin Dfx This domain is found as essentially the full length of desulforedoxin, a 37-residue homodimeric non-haem iron protein. It is also found as the N-terminal domain of desulfoferrodoxin (rbo), a homodimeric non-haem iron protein with 2 Fe atoms per monomer in different oxidation states. This domain binds the ferric rather than the ferrous Fe of desulfoferrodoxin. Neelaredoxin, a monomeric blue non-haem iron protein, lacks this domain.