Location of haem in bacterioferritin of E. coli

. A low‐resolution partial structure of bacterioferritin was solved using a combination of molecular replacement and rigid‐body refinement methods. Modification of bacterioferritin crystals by soaking in tetrachloroplatinate results in a phase transition from tetragonal symmetry (space group P42212) to a pseudo‐cubic one (approximate space group I432). Helical parts of human H ferritin structure stripped of side chains beyond the Cβ atoms were used as the model. An electron‐density map of the refined model revealed a region of extended density which by its shape and position in a pocket between helices was identified as haem. Inclusion of haem in the refinement showed that it can occupy only one of two symmetry‐related sites near a twofold axis of the molecule.