Mitochondrial ferritin in animals and plants.

Ferritins play a role in preventing Fe toxicity because of their ability to sequester several thousand Fe atoms in their central cavity in a soluble, non-toxic bioavailable form. The identification of ferritin in mitochondria, an organelle with a constant generation of O2(-) as a by-product of the electron transfer, and the presence of a mitochondrial nitric oxide synthase activity opened up brand new metabolic interactions to be analyzed. In spite of cytosolic ferritins in mammals being ubiquitous, mitochondrial ferritin (mtF) expression is restricted to the testis, neuronal cells, islets of Langerhans, and as recently described to mice normal retinas. None was detected in major storage organs such as liver and spleen. MtF has about 80% identity to cytosolic H-chain and 55% to L-chain in its coding region. There has been reported some differences in the Fe binding and oxidation properties between mtF and cytosolic H-ferritin suggesting that mtF functions differently as an Fe storage protein within the mitochondria and perhaps has other function(s) in Fe homeostasis as well. Recently it was also presented evidence for the presence of ferritins in plant mitochondria. The understanding of the role of mitochondrial ferritin in Fe oxidative metabolism may be useful in approaching clinical situations such as the treatment of Friedreich's ataxia, X-linked sideroblastic anemia, and in other neurodegenerative disorders.