Iron deposition in apoferritin. Evidence for the formation of a mixed valence binuclear iron complex.

This study investigates iron deposit behavior in a protein called apoferritin, revealing the formation of structures with different iron charges which may be crucial steps in iron core formation within proteins.

Overview of the Research

• Using an investigative technique called Electron Paramagnetic Resonance (EPR), this study explores how iron accumulates in apoferritin, a protein that stores iron.
• The iron creates paramagnetic species during the early stages of iron deposition within the shell of the protein, described as paramagnetic because they are attracted to magnetic fields due to the iron presence.
• The paper explains a phenomenon where the iron may exist in different charged states (Fe2+ and Fe3+), forming a mixed valence dimer structure, a complex of two iron ions with different charges.

Key Findings of the Study

• The researchers note the appearance of a “solitary high spin Fe3+ ions” resonance when a certain amount of Fe(II) is added to the apoferritin protein and followed by air oxidation. This resonance accounts for approximately 36% of the added iron.
• However, iron that does not contribute to this resonance is probably present as oligomeric Fe3+ species, complexes of several Fe3+ ions that are not easily detectable by EPR.
• Interestingly, adding even more iron under anaerobic conditions (without air) led to the creation of another iron resonance with special characteristics. This was interpreted as the formation of mixed valence dimers – Fe(II)-Fe(III).
• The new signal was observed only at very low temperatures and was resistant to saturation, suggesting that it arises from spin-coupled Fe(II)-Fe(III) dimers,
• The signal created by this dimer disappears when oxygen is introduced presumably due to oxidation of Fe(II).

Significance of the Research

• The discovery of a spin-coupled iron dimer offers insights into the process of iron core formation within proteins. This can help to further comprehend the role of apoferritin and other similar proteins in iron storage and metabolism.
• Furthermore, understanding how iron behaves in biological systems could lead to better strategies in treating iron-related disorders and improving drug design.