Spectrophotometric competition study between molybdate and Fe(III) hydroxide on N,N'-bis(2,3-dihydroxybenzoyl)-L-lysine, a naturally occurring siderophore synthesized by Azotobacter vinelandii

The solubilization of Fe(III) hydroxide by the naturally occurring siderophore N,N'-bis(2,3-dihydroxybenzoyl)-L-lysine has been investigated spectrophotometrically in the presence and the absence of a stoichiometric amount of molybdate in aqueous medium at pH 7. In the absence of molybdate the reaction is 50% complete after 115 min. In contrast, the addition of an equimolar amount of molybdate results in an instantaneous formation of the molybdenum siderophore complex and a significant delay in the formation of the corresponding iron complex: 50% of the iron complex is present after 44 h and equilibrium is only reached after 2 weeks. The results are discussed with regard to metal acquisition by the nitrogen fixing cells of Azotobacter vinelandii.