Siderophores.

Siderophores, defined as low-iron-induced virtually ferric-specific ligands, are widely distributed in microbial species where they function in the sequestration and transport of iron. In Escherichia coli biosynthesis of siderophores is negatively regulated at the transcriptional level by ferrous ion in conjunction with a repressor protein, Fur (ferric uptake regulation). Siderophores are a component of the virulence armamentarium of clinical isolates of E. coli and of certain other microorganisms pathogenic to man, animals, and plants. The mechanism whereby cells accumulate sufficient iron for activation of essential enzymes while, at the same time, avoiding excess of a potentially toxic element remains one of the most challenging problems in biochemistry.