Other Siderophores

Chelators of iron, which are now widely applied for the treatment of patients with thalassemia and other pathologies associated with iron overload, are the intravenous chelator desferal (desferrioxamine) and oral chelator deferiprone (LI) (Figure 19.23, see also Chapter 31). Desferrioxamine (DFO) belongs to a class of natural compounds called siderophores produced by microorganisms. The antioxidant activity of DFO has been studied and compared with that of synthetic hydroxypyrid-4-nones (LI) and classic antioxidants (vitamin E). It is known that chronic iron overload in humans is associated with hepatocellular damage. Therefore, Morel et al. [370] studied the antioxidant effects of DFO, another siderophore pyoverdin, and hydroxypyrid-4-ones on lipid peroxidation in primary hepatocyte culture. These authors found that the efficacy of chelators to inhibit iron-stimulated lipid peroxidation in hepatocytes decreased in the range of DFO > hydroxypyrid-4-ones > pyoverdin. It seems that other siderophores are also less effective inhibitors of lipid peroxidation than DFO [371],... 

Pyoverdin and other siderophores from bacteria-that mediate iron uptake... 

The product of step o is known as isochoris-mate.55 56 Isochorismate gives rise to a variety of products including vitamin K, salicylic acid,56a the iron chelator enterobactin (Fig. 16-1), and other siderophores. These are formed in E. coli via 2,3-dihy-droxybenzoate as indicated in Fig. 25-2.57-59a The genes (ent) for the requisite enzymes are clustered at 14 min on the E. coli chromosome map (Fig. 26-4). 

The Fur (Ferric uptake regulation) protein is a negative regulator of the aerobactin-operon and of several other siderophore-mediated, high affinity iron transport systems in... 

Despite the wealth of information on siderophores, there is still considerable debate as to how they function in the plant rhizosphere and the degree to which they accumulate in soils. Much of this debate has been due to inadequate methodology for detecting siderophores at microsite locations in the rhizosphere and the lack of analytical methods for in situ study of the interaction of siderophores and other iron mobilizing substances. Using simplified systems in the laboratory, it is possible to examine many different scenarios as to how siderophores might function. Yet, for the most part, there is still almost no information... 

Plant and microbial competition for iron involves very complex interactions that are influenced by a number of factors (Fig. 2). These include differences in the level of siderophore production by all of the competing microorganisms, the chciTiical stabilities of various siderophores and other chelators with iron, their... 

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