Ferritiniron

Ferritiniron is a term that informally describes the iron stored within ferritin, the protein complex that serves as a cellular iron reservoir. Ferritin comprises a hollow protein shell made of 24 subunits that assemble into a nanocage. Inside this cavity, iron is stored in a mineral form, typically ferrihydrite-like ferric oxide, within up to about 4,500 iron atoms per ferritin molecule. This stored iron is mobilizable when the cell needs it for processes such as heme and iron-sulfur cluster synthesis.

Iron entry and storage in ferritin involve specific steps. Fe2+ ions enter the ferritin cavity through channel-like pores. The ferroxidase centers, primarily in H-type subunits, catalyze the oxidation of Fe2+ to Fe3+. The resulting Fe3+ is incorporated into the growing mineral core. The mineral core remains within the ferritin shell, isolated from the cellular environment to minimize iron-initiated reactive oxygen species formation. When iron is needed, the iron is reduced back to Fe2+ and released from the core, exiting the ferritin through the same channels or related pathways.

Physiological role and regulation are centered on iron homeostasis. Ferritin iron acts as a buffer, preventing excess free iron while supplying iron for metabolic needs. Ferritin expression is regulated at the post-transcriptional level by iron regulatory proteins that bind iron-responsive elements in ferritin mRNA. Serum ferritin, largely derived from cellular ferritin, serves as a clinical marker of iron stores but can be elevated in inflammation and liver disease, independent of iron status.

In research and biotechnology, ferritin nanoparticles are explored for targeted drug delivery, imaging, and as models for studying iron metabolism due to their biocompatibility and well-defined structure.