  Synthetic biological macromolecule of magnetoferritin containing an iron
oxide core inside a protein shell (apoferritin) is prepared with different
content of iron. Its structure in aqueous solution is analyzed by small-angle
synchrotron X-ray (SAXS) and neutron (SANS) scattering. The loading factor (LF)
defined as the average number of iron atoms per protein is varied up to LF=800.
With an increase of the LF, the scattering curves exhibit a relative increase
in the total scattered intensity, a partial smearing and a shift of the match
point in the SANS contrast variation data. The analysis shows an increase in
the polydispersity of the proteins and a corresponding effective increase in
the relative content of magnetic material against the protein moiety of the
shell with the LF growth. At LFs above ~150, the apoferritin shell undergoes
structural changes, which is strongly indicative of the fact that the shell
stability is affected by iron oxide presence.
