Azomonas and Azotobacter Siderophores

Azomonas macrozytogenes produces a siderophore with an isopyoverdin chromophore, azoverdin, but with a peptide chain 7 related to those of azotobactins, viz. 236). 

The three-dimensional structure of the Ga complex was determined by NMR techniques as outlined above. Also here the metal ion lies at the surface of the complex 377). 

From Azotobacter vinelandii the structures of two siderophores were elucidated. They contain the chromophore Chrd (Fig. 1) and Hse units azotobactin 87-1 (8) (from the three Hse in this sequence two are l and one d configured) from the strain ATCC 12837 314), and azotobactin D (9) (76) from the strain CCM 289. 

Both of them are accompanied by compounds where the C-teiminal Hse forms a y-lactone ring (azotobactin 87-11 and 8). An azotobactin O for which also a structure had been proposed (720) was shown later to be identical with azotobactin D (272). For secondary metabolites see protochelin and its constituents (Sect. 3.2). 

Azotobacter chroococcum produces ornithine-containing hydroxamate sidero-phores with molecular masses 800 and 844 Da (difference of one carboxyl group ) of unknown structure (115a). 

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