DAHP synthetase I/KDSA Members of the 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthetase family catalyse the first step in aromatic amino acid biosynthesis from chorismate. Class I includes bacterial and yeast enzymes; class II includes higher plants and various microorganisms (see <db_xref db="INTERPRO" dbkey="IPR002480"/>) [<cite idref="PUB00006352"/>]. <p>The first step in the common pathway leading to the biosynthesis of aromatic compounds is the stereospecific condensation of phosphoenolpyruvate (PEP) and D-erythrose-4-phosphate (E4P) giving rise to 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP). This reaction is catalyzed by DAHP synthase, a metal-activated enzyme, which in microorganisms is the target for negative-feedback regulation by pathway intermediates or by end products. In <taxon tax_id="562">Escherichia coli</taxon> there are three DAHP synthetase isoforms, each specifically inhibited by one of the three aromatic amino acids. The crystal structure of the phenylalanine-regulated form of DAHP synthetase shows the fold as is a (beta/alpha)8 barrel with several additional beta strands and alpha helices [<cite idref="PUB00006452"/>]. </p>