LOCATION OF HEME IN BACTERIOFERRITIN OF ESCHERICHIA-COLI

A low-resolution partial structure of bacterioferritin was solved usin g a combination of molecular replacement and rigid-body refinement met hods. Modification of bacterioferritin crystals by soaking in tetrachl oroplatinate results in a phase transition from tetragonal symmetry (s pace group P4(2)2(1)2) to a pseudocubic one (approximate space group I 432). Helical parts of human H ferritin structure stripped of side cha ins beyond the c(beta) atoms were used as the model. An electron-densi ty map of the refined model revealed a region of extended density whic h by its shape and position in a pocket between helices was identified as haem. Inclusion of haem in the refinement showed that it can occup y only one of two symmetry-related sites near a twofold axis of the mo lecule.