Fig. 6. Electrostatic potential surfaces of Dd Bfr (A and B; PDB 1nfv), Ec Bfr (C and D; PDB 1bcf) and Ec ferritin (E and F; PDB 1eum). (A, C and E) Views down a 4-fold axis (non-crystallographic). (B, D and F) Views down a 3-fold axis (crystallographic for Dd Bfr, non-crystallographic for Ec Bfr and Ec ferritin). The molecular surfaces were calculated with MSMS (Sanner et al., 1996) using a probe radius of 1.4 Å (1.2 Å for Ec Bfr). The electrostatic potentials were calculated with MEAD (Bashford, 1997) using protein and external dielectric constants of 4 and 80, respectively, a temperature of 300 K and an ionic strength of 0.1 M; for Dd Bfr, +3 charges were assumed for all the iron atoms; for Ec Bfr, +2 charges were assumed for the manganese atoms and +3 for the haem iron atoms; for Ec ferritin, no metal ions were included in the calculations as none is present in the deposited coordinates. FP, ferroxidase pore; MC, major channel; NC2, 2-fold non-crystallographic axis.