Iron is both a nutritious and potentially noxious element. Its precise regulation in cells is necessary to assure synthesis of several proteins of which the metal is an integral part. At the same time, the cell must avoid generation of tissue-damaging oxygen radicals, which are known to arise from certain transition metals, such as iron.

Environmental iron is mostly in a form (the 3+ oxidation state) that is characterized by extreme insolubility at biological pH. In order to dissolve iron, many bacterial and fungal species synthesize a line of relatively low molecular weight, virtually ferric-specific chelating, or binding, agents generically called siderophores (Gr. “iron bearer,” ISI Atlas of Science: Biochemistry, 1, 53-6, 1988). The affinity of siderophores for iron (III) is such that they can compete effectively with hydroxyl ion for the metal. Microorganisms have also evolved highly efficient transport systems for ferric siderophores that enable them to recognize...

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