FIG. 2.
A model of Escherichia coli fumarate and nitrate reduction (FNR) regulator and its reaction with O2. The FNR model is based on the structure of E. coli catabolite repressor protein (CRP) [pdb file 1CGP (126)]. The [4Fe-4S] cluster is represented by a cube. After the increase in O2 concentration, the DNA-bound dimer FNR protein undergoes reaction at its cluster, resulting in a [2Fe-2S] form (represented by a rhomb) that dissociates into monomers and no longer binds DNA.