Pseudomonas aeruginosa possesses two novel regulatory isozymes of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase

• Published in: The Journal of biological chemistry Vol. 257; no. 21; pp. 12789 - 12794
• Main Authors: Whitaker, R J, Fiske, M J, Jensen, R A
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 10.11.1982; American Society for Biochemistry and Molecular Biology
• Subjects: 3-Deoxy-7-Phosphoheptulonate Synthase - isolation & purification; 3-Deoxy-7-Phosphoheptulonate Synthase - metabolism; Aldehyde-Lyases - metabolism; Isoenzymes - isolation & purification; Isoenzymes - metabolism; Kinetics; Molecular Weight; Pseudomonas aeruginosa - enzymology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)33582-8

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.