Fig. 25.22 Crystal structure of actinonin 25.75 with the peptide deformylase from Escherichia coli. The peptidic inhibitor binds to the Fe2+ ion with its hydroxamate function. Its n-pentyl chain replaces the methionine side chain in the natural substrate and lies in the deeply buried S1′ pocket. The iron ion is bound to a cysteine and two histidines.