Abstract
Iron biomineralization occurs in a variety of forms in many different organisms. These processes, ranging from magnetite formation in magnetotactic bacteria to the formation of the ferritin iron core in mammalian liver, all require certain fundamental mechanisms of cellular iron metabolism. These include the transport of exogenous iron into the cell, storage and detoxification of intracellular iron, and intracellular transport and compartmentalization of the metal. Exogenous iron transport systems have been well characterized in many organisms1. In vertebrates, iron is transported in serum bound to the transferrin protein. This complex binds to cell surface receptors and the iron is passed across the plasma membrane into the cell. Many microbes produce compounds called siderophores that serve a role similar to transferrin, binding iron with high affinity and interacting with cell surface receptors to bring iron to the cell. The path of the metal inside the cell is not well understood. It is clear that in higher eukaryotes, the iron-binding protein ferritin stores iron in specialized tissues such as the liver. It is not known, however, what role ferritin plays in iron storage or detoxification in other cells.