Binding of the ferric uptake regulation repressor protein (Fur) to Mn(II), Fe(II), Co(II), and Cu(II) ions as co-repressors: electronic absorption, equilibrium, and 57Fe Mössbauer studies.

The binding of the repressor protein (Fur) to Fe(II) as co-repressor was studied. Other transition metal ions such as Mn(II), Co(II), and Cu(II) were also studied as models. From the equilibrium studies Kd values of 55, 85, 36, and 10 microM were obtained for the Fur complex with Fe(II), Mn(II), Co(II), and Cu(II), respectively. The ratio of metal to Fur monomer was 1:1 in both the Fe(II) and Mn(II) complexes. Fur mutants were also studied. Electronic absorption spectra of the Co(II) Fur complex gave evidence of a distorted tetrahedral Co(II) site bound to sulfur. Frozen solution 57Fe Mössbauer spectra of the Fe(II) Fur indicated the presence of Fe(II) in a high spin distorted octahedral environment. The role of the metal ion as co-repressor in the binding of Fur to DNA is discussed in view of the above results.