Quaternary structure of apoferritin: the rotation function at 9 A resolution

The rotation function has been calculated for apoferritin using data at 9 Å resolution obtained from cubic crystals, space group F432, and compared with rotation functions of possible alternative model structures consisting of (a) 24 subunits at the vertices of a snub-cube (octahedral symmetry) and (b) 20 subunits at the vertices of a pentagonal dodecahedron (icosahedral symmetry). The apoferritin rotation function, like that of the 24 subunit model, had large peaks only on the crystallographic rotation axes. The 20 subunit model gave peaks on non-crystallographic axes, which were not observed with apoferritin. It is concluded that apoferritin molecules consist of 24 subunits arranged in 432 (octahedral) symmetry as suggested by the space group.