Iron-storage protein, whose ferroxidase center binds Fe(2+) ions, oxidizes them by dioxygen to Fe(3+), and participates in the subsequent Fe(3+) oxide mineral core formation within the central cavity of the protein complex. The mineralized iron core can contain as many as 2700 iron atoms/24-meric molecule. 4 Fe(2+) + 4 H(+) + O2 = 4 Fe(3+) + 2 H2O Binds 1 heme b (iron(II)-protoporphyrin IX) group per dimer. Binds 2 iron ions per subunit. The catalytic dinuclear iron-binding site within each subunit is known as the ferroxidase center. In BFR, the ferroxidase center appears to function as a true di-iron catalytic cofactor, rather than as a pore for the transfer of iron into the central cavity, as found for eukaryotic ferritins. Iron oxidation is inhibited by Zn(2+), which binds at the ferroxidase center with a higher affinity that Fe(2+). The occupation of the ferroxidase center by Zn(2+) also severely restricts the ability of BFR to form an iron core. Homooligomer of 24 subunits, arranged as 12 dimers, that are packed together to form an approximately spherical molecule with a central cavity, in which large amounts of iron can be deposited as a ferric-oxy-hydroxide mineral core. The internal surface iron site that binds iron 3 is important for the mineralization phase but not for Fe(2+) binding and oxidation at the ferroxidase center. Belongs to the bacterioferritin family.