title: Pseudomonas aeruginosa possesses two novel regulatory isozymes of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase.
abstract: In Pseudomonas aeruginosa the initial enzyme of aromatic amino acid biosynthesis, 3-deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) synthase, has been known to be subject to feedback inhibition by a metabolite in each of the three major pathway branchlets. Thus, an apparent balanced multieffector control is mediated by L-tyrosine, by L-tryptophan, and phenylpyruvate. We have now resolved DAHP synthase into two distinctive regulatory isozymes, herein denoted DAHP synthase-tyr (Mr = 137,000) and DAHP synthase-trp (Mr = 175,000). DAHP synthase-tyr comprises greater than 90% of the total activity. L-Tyrosine was found to be a potent effector, inhibiting competitively with respect to both phosphoenolpyruvate (Ki = 23 microM) and erythrose 4-phosphate (Ki = 23 microM). Phenylpyruvate was a less effective competitive inhibitor: phosphoenolpyruvate (Ki = 2.55 mM) and erythrose 4-phosphate (Ki = 1.35 mM). DAHP synthase-trp was found to be inhibited noncompetitively by L-tryptophan with respect to phosphoenolpyruvate (Ki = 40 microM) and competitively with respect to erythrose 4-phosphate (Ki = 5 microM). Chorismate was a relatively weak competitive inhibitor: phosphoenolpyruvate (Ki = 1.35 mM) and erythrose 4-phosphate (Ki = 2.25 mM). Thus, each isozyme is strongly inhibited by an amino acid end product and weakly inhibited by an intermediary metabolite.
mesh_terms: D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000302:isolation & purification / Q000378:metabolism*; D000446:Aldehyde-Lyases / Q000378:metabolism*; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D011550:Pseudomonas aeruginosa / Q000201:enzymology*
chemical_list: D007527:Isoenzymes; D010723:3-Deoxy-7-Phosphoheptulonate Synthase; D000446:Aldehyde-Lyases