title: Enzymic arrangement and allosteric regulation of the aromatic amino acid pathway in Neisseria gonorrhoeae.
abstract: The pathway construction and allosteric regulation of phenylalanine and tyrosine biosynthesis was examined in Neisseria gonorrhoeae. A single 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase enzyme sensitive to feedback inhibition by L-phenylalanine was found. Chorismate mutase and prephenate dehydratase appear to co-exist as catalytic components of a bifunctional enzyme, known to be present in related genera. The latter enzyme activities were both feedback inhibited by L-phenylalanine. Prephenate dehydratase was strongly activated by L-tyrosine. NAD+-linked prephenate dehydrogenase and arogenate dehydrogenase activities coeluted following ion-exchange chromatography, suggesting their identity as catalytic properties of a single broad-specificity cyclohexadienyl dehydrogenase. Each dehydrogenase activity was inhibited by 4-hydroxyphenylpyruvate, but not by L-tyrosine. Two aromatic aminotransferases were resolved, one preferring the L-phenylalanine:2-ketoglutarate substrate combination and the other preferring the L-tyrosine: 2-ketoglutarate substrate combination. Each aminotransferase was also able to transaminate prephenate. The overall picture of regulation is one in which L-tyrosine modulates L-phenylalanine synthesis via activation of prephenate dehydratase. L-Phenylalanine in turn regulates early-pathway flow through inhibition of DAHP synthase. The recent phylogenetic positioning of N. gonorrhoeae makes it a key reference organism for emerging interpretations about aromatic-pathway evolution.
mesh_terms: D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000378:metabolism; D055598:Chemical Phenomena; D002621:Chemistry; D002852:Chromatography, Ion Exchange; D006801:Humans; D006836:Hydro-Lyases / Q000378:metabolism; D009344:Neisseria gonorrhoeae / Q000201:enzymology* / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism*; D010649:Phenylalanine / Q000096:biosynthesis*; D011303:Prephenate Dehydrogenase / Q000378:metabolism; D000637:Transaminases / Q000378:metabolism*; D014443:Tyrosine / Q000096:biosynthesis*; D014444:Tyrosine Transaminase / Q000378:metabolism
chemical_list: D014443:Tyrosine; D010649:Phenylalanine; D010088:Oxidoreductases; D011303:Prephenate Dehydrogenase; D010723:3-Deoxy-7-Phosphoheptulonate Synthase; C040713:3-phenylpyruvate aminotransferase; D000637:Transaminases; C044954:prephenate aminotransferase; D014444:Tyrosine Transaminase; D006836:Hydro-Lyases; C022437:pretyrosine dehydratase