Iron, an essential element for biosynthesis of aromatic compounds.

Homogeneous preparations of 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase [7-phospho-2-keto-3-deoxy-D-arabino-heptonate D-erythrose-4-phosphate lyase (pyruvate phosphorylating), EC 4.1.2.15] isolated as the enzyme-phosphoenolpyruvate complex from Escherichia coli are shown by atomic absorption analysis to contain approximately one mole of iron per mole of native enzyme. No cobalt was found, in contrast to suggestions of earlier workers. Pure enzyme preparations show a unique absorption maximum around 350 nm with an epsilon value of about 3500 M-1cm-1. The 350-nm band as well as the enzyme activity is lost when the enzyme is denatured with guanidine-hydrochloride, or when phosphoenolpyruvate, the first substrate to bind to the enzyme, is totally removed from the enzyme by incubation with an excess of erythrose 4-phosphate, the second substrate to bind to the enzyme. The iron remains bound to the enzyme when phosphoenolpyruvate is removed from the enzyme-phosphoenolpyruvate complex.