Mugeneic acid

Figure 7.8 Structure of the phytosiderophore mugeneic acid and its precursor nicotianamine.

As described in an earlier section, transport problems posed by the six elements listed in the heading are somewhat simpler (with the exception of chromium) than those for iron. One very interesting recent development has been the characterization of sequestering agents produced by plants which complex a number of metal ions, not just ferric ions. A key compound, now well-characterized, is mugeneic acid (Figure 1.17)." The structural and chemical similari-... 

Structure and a stereo view of mugeneic acid. See Reference 42. 

Molecular structures of the complexes (molecules A and B) and coordination about the cobalt ion in molecules A and B of the mugeneic acid-Co(III) complex. Bond lengths in A angles in degrees. See Reference 42. 

Iron is transported in forms in which it is tightly complexed to small chelators called siderophores (microorganisms) or to proteins called transferrins (animals) or to citrate or mugeneic acid (plants). The problem of how the iron is released in a controlled fashion is largely unresolved. The process of mineral formation, called biomineralization, is a subject of active investigation. Vanadium and molybdenum are transported as stable anions. Zinc and copper appear to be transported loosely associated with peptides or proteins (plants) and possibly mugeneic acid in plants. Much remains to be learned about the biological transport of nonferrous metal ions. 

There is no evidence for siderophore-like molecules in multicellular animals, and vHth the exception of grasses and the related cereals, there is no evidence for the existence of siderophores in plants. Grasses secrete phyto-siderophores, for instance, mugeneic acid 6. into the soil under low iron conditions and. consequently, are able to thrive in alkaline soils. 

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