Iron binding of primary iron-sulphur cluster assembly proteins. Iron-sulphur cluster assembly proteins IscS, IscU, IscA, HscB and HscA were purified from E. coli cells grown in LB media. a), iron content of purified iron-sulphur cluster assembly proteins. Iron content was presented as the ratio of iron atoms per protein dimer. b), iron content of iron-sulphur cluster assembly proteins (50 μM in monomer) after incubation with Fe(NH4)2(SO4)2 (50 μM), sodium citrate (5 mM) and dithiothreitol (2 mM). Proteins were re-purified from incubation solutions. Iron content was presented as the ratio of iron atoms per protein dimer. The data are averages plus standard deviations from three independent experiments.