Ferritin is a ubiquitous protein that plays a critical role in regulating intracellular iron
homoeostasis by storing iron inside its multimeric shell. It also plays an important role in
detoxifying potentially harmful free ferrous iron to the less soluble ferric iron by virtue of the
ferroxidase activity of the H subunit. Although excess iron is stored primarily in cytoplasm,
most of the metabolically active iron in cells is processed in mitochondria. Little is yet known
of how these organelles regulate iron homeostasis and toxicity. Here we report an unusual …