Question regarding an Escherichia coli reaction
As far as I can tell, enterochelin esterase (Fes) utilizes an Alpha/Beta hydrolase fold to catalyze it's reactions, which means there's a triad of catalytic amino acid side chains. Where Fes differs from other proteins in the pathway is an amino terminal lid domain which confers specificity to the substrates of Fes ((1) dictates this forms a deep pocket in the protein). I'm having trouble finding the exact catalytic amino acids, but homology modeling between IroE and Fes from the same source shows this may be a triad of Glu, His and Ser. If we kind of visualize what a catalytic triad's mechanism looks like, and the following image is a generic lipase/esterase catalytic site,



A sort of transition state is formed between the target molecule and the serine, where the water reacts with help from the asp/glu and histidine to catalyze the hydrolysis. You'd just call it protein-ligand interactions.