Morphology and magnetic structure of the ferritin core during iron loading and releasing by magnetooptical and NMR methods.

The ferritin is a protein, which serves as a storage and transportation capsule for iron inside living organisms. Continuous charging protein with iron and releasing it from the ferritin is necessary to assure proper management of this important ions within organism. From other side synthetic ferritin have great potential for biomedical and technological applications. In this work the behavior of ferritin during the processes of iron loading and releasing was examined using multiplicity of experimental technique. The quality of protein's shell was monitored using circular dichroism, whereas the average size and its distribution was estimated from dynamic light scattering and TEM images, respectively. Because of the magnetic behavior of the iron mineral, number of magnetooptical methods were used to gain information on the iron core of the ferritin. Faraday rotation and magnetic linear birefringence studies provides evidence that the iron loading and the iron release processes are not symmetrical. The spatial organization of the mineral within the protein's core changes depending on whether the iron was incorporated to, or removed from the ferritins shell. Magnetic optical rotatory dispersion spectra exclude contribution of Fe(II)-composed mineral, whereas joined magnetooptical and NMR results indicate that no mineral with high magnetization appear at any stage of the loading/release process. These findings suggest that the iron core of loaded/released ferritin consists of single-phase i.e. ferrihydrite. Presented results demonstrate usefulness of emerging magnetooptical methods in biomedical research and applications.