3-Deoxy-D-arabino-heptulosonic acid 7-phosphate synthase mutants of Salmonella typhimurium.
The first committed step of aromatic amino acid biosynthesis in Salmonella typhimurium was shown to be catalyzed by three isoenzymes of 3-deoxy-D-arabino-heptulosonic acid 7-phosphate (DAHP) synthase. Mutations in each of the genes specifying the isoenzymes were isolated and mapped. aroG, the structural gene for the phenylalanine-inhibitable isoenzyme, was linked to gal, and aroH, the structural gene for the tryptophan-inhibitable isoenzyme, was linked to aroE. aroF, the structural gene for the tyrosine-inhibitable isoenzyme, was linked to pheA and tyrA, which specify the phenylalanine- and tyrosine-specific branch-point enzymes, respectively. The phenylalanine-inhibitable isoenzyme was the predominant DAHP synthase in wild-type cells, and only the tryosine-inhibitable isoenzyme was completely repressed, as well as inhibited, by low levels of its allosteric effector. The DAHP synthase isoenzymes were separated by chromatography on diethylaminoethyl-cellulose with a phosphate gradient which contained enolpyruvate phosphate to protect the otherwise unstable phenylalanine-inhibitable isoenzyme. No cross-inhibition of either the tyrosine- or phenylalanine-inhibitable isoenzyme was observed at inhibitor concentrations up to 1 mM. The tryptophan-inhibitable isoenzyme was partially purified from extracts of a strain lacking the other two isoenzymes and shown to be inhibited about 30% by 1 mM tryptophan. A preliminary study of interference by tryptophan in the periodate-thiobarbiturate assay for DAHP suggested a combined effect of tryptophan and erythrose 4-phosphate, or an aldehydic compound resulting from degradation of erythrose 4-phosphate by periodate.
D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D000446:Aldehyde-Lyases / Q000096:biosynthesis*; D002474:Cell-Free System; D002848:Chromatography, DEAE-Cellulose; D002874:Chromosome Mapping; D005796:Genes; D006037:Glyoxal / Q000494:pharmacology; D007527:Isoenzymes / Q000096:biosynthesis* / Q000302:isolation & purification / Q000378:metabolism; D009154:Mutation; D010649:Phenylalanine / Q000378:metabolism; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000378:metabolism; D013403:Sugar Phosphates / Q000494:pharmacology; D013780:Tetroses; D014364:Tryptophan / Q000378:metabolism / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D007527:Isoenzymes; D013403:Sugar Phosphates; D013780:Tetroses; D014443:Tyrosine; D010649:Phenylalanine; D006037:Glyoxal; D014364:Tryptophan; D010723:3-Deoxy-7-Phosphoheptulonate Synthase; D000446:Aldehyde-Lyases