In Vitro Iron Release From Intact Ferritin Protein Nanocages: Impact of Physiological Reducing Agents and the Ascorbate‐Quinone Redox Couple

Ferritin, an iron-storage protein, plays a crucial role in the management of cellular iron homeostasis and prevents iron-induced toxicity. It rapidly sequesters free Fe²⁺ and synthesizes soluble protein-caged ferric-mineral, while ensuring controlled iron-release upon cellular requirements. Given the reducing environment of the cytosol, reductive dissolution of ferritin bio-mineral is considered one of the plausible iron release pathway in vivo. NADH (∼ 0.1-0.3 mM), GSH (∼ 1-8 mM), and AscH₂ (∼ 0.1 mM) mostly contribute toward this redox milieu. The current work investigates the effectiveness of these reductants in promoting iron mobilization from ferritin in vitro. Ascorbate was found to release the highest amount of iron, even at its lower physiological concentrations. To further enhance iron-release efficiency, a series of quinones, varying in structure and redox potential, were employed as electron mediators along with ascorbate (electron-source). While certain quinones enhanced the process, others inhibited it. Our findings highlight that ascorbate/quinone-mediated iron release from ferritin is largely dictated by the molecular structure and the reduction potentials of quinones. This study may provide insights into the redox behavior of quinones, in vivo iron release pathways and also strengthen our understanding on other biological ET processes and O₂-based cellular toxicity.