Siderophore Mediated Iron(III) Uptake in Gliocladium virens: 1. Properties of cis-Fusarinine, trans-Fusarmine, Dimerum Acid, and Their Ferric Complexes

Abstract

Gliocladium virens (ATCC 24290) produces two monohydroxamates ( cis- and trans-fusarinine) and a dihydroxamate (dimerum acid) as the major siderophores in the culture filtrate. This fungus also produces minor quantities of three trihydroxamates (the deferri forms of ferricrocin, coprogen B, and coprogen). Structural features of the free ligands and the metal complexed forms of cis-fusarinine (cF), trans-fusarinine (tF), and dimerum acid (DA) have been investigated using electronic (visible), circular dichroism (CD), and NMR spectroscopy. In aqueous solution, in the pH range of 6.5–8.0, all of the ferric complexes of cF (and tF) exist as 3:1 chelates. Fe(cF) 3 [or Fe(tF) 3] forms both Λ and Δ coordination isomers, but the former in a slight excess. DA forms a 3:2 ferric complex in the pH range of 5.0–8.0. Iron coordination in Fe 2(DA) 3 is predominantly Δ. DA ligands in Ga 2(DA) 3 exist as two different conformers at a ratio of 2:1. In mixed solution cF, tF, and DA form a large number of homogeneous and heterogeneous Fe(III) chelates.