Electron Transfer from Haem to the Di‐Iron Ferroxidase Centre in Bacterioferritin

The iron redox cycle in ferritins is not completely understood. Bacterioferritins are distinct from other ferritins in that they contain haem groups. It is acknowledged that the two iron motifs in bacterioferritins, the di‐nuclear ferroxidase centre and the haem B group, play key roles in two opposing processes, iron sequestration and iron mobilisation, respectively, and the two redox processes are independent. Herein, we show that in Escherichia coli bacterioferritin, there is an electron transfer pathway from the haem to the ferroxidase centre suggesting a new role(s) haem might play in bacterioferritins. The haem in bacterioferritins has been shown before to provide an electron to the ferritin's mineral core—to reduce Fe3+ to water soluble Fe2+. This work shows that the haem can also provide an electron, over a distance of approximately 13 Å, to the di‐iron ferroxidase centre of the protein, in a redox process not yet known.