(8,9,16,28). These iron hydroxamates are transported across the cytoplasmic membrane by the same transport system composed of the periplasmic FhuD protein, the very hydrophobic transmembrane FhuB protein, and the membrane-associated FhuC protein (8,10,11,16,23,24

The iron(III) transport system via citrate displays the characteristics of a binding protein-dependent transport mechanism through the cytoplasmic membrane. One of the five transport proteins, FecE, contains the two motifs found in ATP-binding proteins. Cloned overexpressed FecE was photoaffinity-labelled with [32P]8-azido-ATP. Labelling was inhibited by 1 mM ATP, ADP, GTP and less by CTP, demonstrating the specificity of the reaction. It is suggested that ATP is the principal energy source for iron(III) citrate transport through the cytoplasmic membrane of Escherichia coli.

The iron(III) transport system via citrate displays the characteristics of a binding protein‐dependent transport mechanism through the cytoplasmic membrane. One of the five transport proteins, FecE, contains the two motifs found in ATP‐binding proteins. Cloned overexpressed FecE was photoaffinity‐labelled with [32P]8‐azido‐ATP. Labelling was inhibited by 1 mM ATP, ADP, GTP and less CTP, demonstrating the specificity of the reaction. It is suggested that ATP is the principal energy source for iron (III) citrate transport through the cytoplasmic membrane of Escherichia coli.