Protects DNA from oxidative damage by sequestering intracellular Fe(2+) ion and storing it in the form of Fe(3+) oxyhydroxide mineral. One hydrogen peroxide oxidizes two Fe(2+) ions, which prevents hydroxyl radical production by the Fenton reaction (By similarity). Both oligomeric forms of dps exhibit ferroxidase activity and DNA binding. Dodecameric dps is capable of Fe(2+) oxidation/mineralization. Only dimeric dps affords efficient DNA protection against hydroxyl radical-mediated cleavage. 2 Fe(2+) + 2 H(+) + H2O2 = 2 Fe(3+) + 2 H2O The 12 subunits form a hollow sphere into which the mineral iron core of up to 500 Fe(3+) can be deposited (By similarity). The homododecameric forms at higher concentration of salt, the homodimeric form under reducing, low-salt conditions. The assembly of the dodecamer is irreversible. 12 di-nuclear ferroxidase centers are located at the interfaces between subunits related by 2-fold symmetry axes. Dodecameric dps forms large aggregates upon binding to DNA. Addition of Ca(2+) to dodecameric dps can result in the reduction of bound Fe(3+). Belongs to the Dps family.