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PubMed1986

Nucleotide sequence of Escherichia coli pyrG encoding CTP synthetase.

The amino acid sequence of Escherichia coli CTP synthetase was derived from the nucleotide sequence of pyrG. The derived amino acid sequence, confirmed at the N terminus by protein sequencing, predicts a subunit of 544 amino acids having a calculated Mr of 60,300 after removal of the initiator methionine. A glutamine amide transfer domain was identified which extends from approximately amino acid residue 300 to the C terminus of the molecule. The CTP synthetase glutamine amide transfer domain contains three conserved regions similar to those in GMP synthetase, anthranilate synthase, p-aminobenzoate synthase, and carbamoyl-P synthetase. The CTP synthetase structure supports a model for gene fusion of a trpG-related glutamine amide transfer domain to a primitive NH3-dependent CTP synthetase. The major 5' end of pyrG mRNA was localized to a position approximately 48 base pairs upstream of the translation initiation codon. Translation of the gene eno, encoding enolase, is initiated 89 base pairs downstream of pyrG. The pyrG-eno junction is characterized by multiple mRNA species which are ascribed to monocistronic pyrG and/or eno mRNAs and a pyrG eno polycistronic mRNA.

Amino Acid Sequence↗
PubMed2000

Increasing tryptophan synthesis in a forage legume Astragalus sinicus by expressing the tobacco feedback-insensitive anthranilate synthase (ASA2) gene.

A cDNA clone that encodes a feedback-insensitive anthranilate synthase (AS), ASA2, isolated from a 5-methyl-tryptophan (Trp) (5MT)-resistant tobacco cell line under the control of the constitutive cauliflower mosaic virus 35S promoter, was introduced into the forage legume Astragalus sinicus by Agrobacterium rhizogenes with kanamycin selection. The 35S-ASA2 gene was expressed constitutively as demonstrated by northern-blot hybridization analyses and the presence of feedback-insensitive AS. Hairy root lines transformed with 35S-ASA2 grew in concentrations of up to 100 microM 5MT, whereas the controls were completely inhibited by 15 microM 5MT. Expression of the feedback-insensitive ASA2 resulted in a 1.3- to 5.5-fold increase in free Trp. Kinetic studies of the AS activity demonstrate the Trp feedback alterations and indicate that the ASA2 alpha-subunit can interact with the native A. sinicus beta-subunit to form an active enzyme. The ASA2 transcript and high free Trp were also detected in the leaves, stems, and roots of plants regenerated from the transformed hairy roots. Thus, we show for the first time that ASA2 can be used to transform plants of a different species to increase the levels of the essential amino acid Trp and impart 5MT resistance.

Anthranilate Synthase↗
PubMed1977

The hydrolysis of flavouring esters by artificial gastrointestinal juices and rat tissue preparations.

The rates of hydrolysis of sixteen esters used as constituents of artifical flavours have been determined in artificial gastrointestinal juices and in fresh preparations of rat liver and small intestine. The artificial gastrointestinal juices exhibited a limited ability to hydrolyse the esters and of which methyl anthranilate was virtually uneffected. On the other hand, rat liver and small intestinal preparations were found readily to hydrolyse the esters to their component acids and alcohols. These findings showing large differences between the results obtained from the two methods suggest that use of tissue preparations is likely to produce data more relevant to the toxicological assessment of esters.

Animals↗
PubMed1970

Enzymes of the tryptophan pathway in Acinetobacter calco-aceticus.

All enzymes of the tryptophan synthetic pathway were detectable in extracts from wild-type Acinetobacter calco-aceticus. The levels of these enzymes were determined in extracts from a number of auxotrophs grown under limiting tryptophan. In each case only anthranilate synthetase was found to be present in increased amounts, whereas the specific activities of the remaining enzymes remained unchanged and unaffected by the tryptophan concentration. Derepression of anthranilate synthetase was found to occur as the concentration of tryptophan became limiting. Anthranilate synthetase and phosphoribosyl transferase activities are both feedback-inhibited by tryptophan. Molecular weight determination carried out by gel filtration and zonal centrifugation in sucrose revealed that all the enzymes are less than 100,000, and no molecular aggregates of these enzymes were detected. The data indicate that tryptophan synthesis in Acinetobacter is regulated both by feedback inhibition of the first two enzymes of the pathway and by repression control of anthranilate synthetase.

Alkaline Phosphatase↗
PubMed2006

Translation control of trpG from transcripts originating from the folate operon promoter of Bacillus subtilis is influenced by translation-mediated displacement of bound TRAP, while translation control of transcripts originating from a newly identified trpG promoter is not.

Bacillus subtilis trpG encodes a glutamine amidotransferase subunit that participates in the biosynthesis of both tryptophan and folic acid. TRAP inhibits translation of trpG in response to tryptophan by binding to a site that overlaps the trpG Shine-Dalgarno sequence, thereby blocking ribosome binding. Similar mechanisms regulate trpP and ycbK translation. The equilibrium binding constants of tryptophan-activated TRAP for the trpG, ycbK, and trpP transcripts were determined to be 8, 3, and 50 nM, respectively. Despite TRAP having a higher affinity for the trpG transcript, TRAP exhibited the least control of trpG expression. The trpG Shine-Dalgarno sequence overlaps the stop codon of the upstream pabB gene, while six of nine triplet repeats within the TRAP binding site are located upstream of the pabB stop codon. Thus, ribosomes translating the upstream pabB cistron could be capable of reducing TRAP-dependent control of TrpG synthesis by displacing bound TRAP. Expression studies using pabB-trpG'-'lacZ fusions in the presence or absence of an engineered stop codon within pabB suggest that translation-mediated displacement of bound TRAP reduces TRAP-dependent inhibition of TrpG synthesis from transcripts originating from the folate operon promoter (P(pabB)). A new trpG promoter (P(trpG)) was identified in the pabB coding sequence that makes a larger contribution to trpG expression than does P(pabB). We found that TRAP-dependent regulation of trpG expression is more extensive for a transcript originating from P(trpG) and that transcripts originating from P(trpG) are not subject to translation-mediated displacement of bound TRAP.

Anthranilate Synthase↗
PubMed1971

Influences of various amino acids on tryptophan-mediated control of the tryptophan biosynthetic enzymes in Escherichia coli.

Lysates of Escherichia coli Ymel obtained from cultures grown in the absence of tryptophan in minimal medium supplemented with 0.1% casein hydrolysate show an approximate fivefold increase in steady-state specific activity of both anthranilate synthetase and tryptophan synthetase A protein relative to cultures grown in nonsupplemented medium. In the presence of repressing levels of exogenous tryptophan, growth of cultures in casein hydrolysate-supplemented medium results in a noncoordinate enhancement of repression of 10-fold for anthranilate synthetase and twofold for tryptophan synthetase A protein. Similar, but less pronounced, effects are shown for strain W3110. Strains possessing tryptophan regulator gene mutations do not exhibit this first effect, but do yield an approximate twofold decrease in specific activity of both enzymes when grown in medium supplemented with tryptophan and casein hydrolysate. A stimulation of derepression of both enzymes in strain Ymel equivalent to that induced by casein hydrolysate can be reproduced by growth in minimal medium supplemented with threonine, phenylalanine, tyrosine, serine, glutamic acid, and glutamine. Doubling time in this medium is not significantly different from that in minimal medium. An enhancement of repression which partially mimics that observed on growth in medium supplemented with tryptophan plus casein hydrolysate is obtained when Ymel is grown on medium supplemented with tryptophan plus methionine. Threonine or phenylalanine plus tyrosine as separate medium supplements are independently capable of producing a 1.4-fold or 3.4-fold stimulation, respectively, but in combination only the phenylalanine plus tyrosine effect is manifested unless serine and glutamic acid or glutamine are included. Our data show that expression of the tryptophan biosynthetic enzymes can be significantly influenced in vivo as a result of growth in medium supplemented with a variety of amino acids.

Amino Acids↗
PubMed1975

Tryptophan metabolism in relation to amino acid alterations during typhoid fever.

With the onset of fever in volunteers exposed to virulent Salmonella typhii as part of a vaccine evaluation study, urinary excretion of kynurenine, acetyl-kynurenine and o-amino-hippurate significantly increased by N-methylnicotinamide decreased. Serum tryptophan concentration at that time was 116% of control in contrast to total serum amino acid values at 83% of control. A 3 gram oral tryptophan load given during illness further increased serum tryptophan concentration to 186% of control and enhanced excretion of the aforementioned catabolites. In addition, urinary anthranilate glucuronide, kynurenate and xanthurenate rose significantly; 3-hydroxykynurenine increased only slightly and N-methyl-nicotinamide was unaltered. Thus, though a tryptophan load aids in detection of alterations in tryptophan catabolism via the kynurenine pathway as a whole, it also distorts the pattern of metabolites detected, seemingly by causing more kynurenine to be shunted to the mitochondria to be acted upon by kynurenine 3-hydroxylase and kynurenine aminotransferase. In unloaded patients the increased urinary excretion of tryptophan metabolites during typhoid fever merely reflect the enhanced flux of amino acids from muscle to liver, akin to that noted in other infections, in excess of that needed for the synthesis of serum proteins or for other metabolic pathways.

Amino Acids↗
PubMed1992

Rhizobium meliloti mutants unable to synthesize anthranilate display a novel symbiotic phenotype.

Analyses of Rhizobium meliloti trp auxotrophs suggest that anthranilate biosynthesis by the R. meliloti trpE(G) gene product is necessary during nodule development for establishment of an effective symbiosis. trpE(G) mutants, as well as mutants blocked earlier along this pathway in aromatic amino acid biosynthesis, form nodules on alfalfa that have novel defects. In contrast, R. meliloti trp mutants blocked later in the tryptophan-biosynthetic pathway form normal, pink, nitrogen-fixing nodules. trpE(G) mutants form two types of elongated, defective nodules containing unusually extended invasion zones on alfalfa. One type contains bacteroids in its base and is capable of nitrogen fixation, while the other lacks bacteroids and cannot fix nitrogen. The trpE(G) gene is expressed in normal nodules. Models are discussed to account for these observations, including one in which anthranilate is postulated to act as an in planta siderophore.

Chromosome Deletion↗
PubMed2005

Metabolic profiling of tryptophan-overproducing rice calli that express a feedback-insensitive alpha subunit of anthranilate synthase.

The profile of aromatic metabolites in calli was compared between wild-type rice (Oryza sativa cv. Nipponbare) and tryptophan-overproducing transgenic rice lines that express a gene (OASA1D) for a feedback-insensitive alpha subunit of anthranilate synthase. Metabolic profiling by high-performance liquid chromatography coupled with photodiode array detection of ultraviolet absorbance revealed a total of 71 peaks in both wild-type and transgenic calli. Only a limited effect on the pattern of major aromatic compounds was observed in tryptophan-accumulating transgenic rice lines, with the exception of an approximately 80-fold increase in the amount of tryptophan. Expression of OASA1D induced relatively small changes in several minor metabolites. One of the minor metabolites whose abundance was increased by OASA1D expression was purified and identified as a previously unknown indole-alkaloid glucoside. The levels of free and conjugated forms of indole-3-acetic acid (IAA), a plant hormone derived from the tryptophan biosynthetic pathway, were determined separately by liquid chromatography and tandem mass spectrometry (LC-MS/MS). The amounts of both free IAA and its conjugates were increased in the transgenic calli, suggesting that the activity of anthranilate synthase or the concentration of tryptophan (or both) is an important determinant of IAA biosynthesis.

Anthranilate Synthase↗
PubMed1979

The metabolism of floctafenin in man and rodents.

Floctafenin (FFn), 2,3-dihydroxypropyl--N--(8--trifluoromethyl--4--quinolyl) anthranilate, a new nonnarcotic analgesic drug, was studied in man, mice, and the isolated perfused rat liver. In all species the drug is rapidly hydrolyzed to floctafenic acid (FFa). In seven volunteer subjects who each received a single oral dose of 400 mg floctafenin on an empty stomach, the blood concentration of FFa usually reached a maximum between 1 and 2 hours (mean 1.57 +/- 1.28 microgram/ml at 1.5 hours) and declined over the next 6 hours. Eight hours after drug administration the mean concentration of FFa in the blood of the volunteers was 0.1 +/- .05 microgram/ml. Approximately 25 per cent of the administered dose of floctafenin was recovered as FFa and hydroxy-FFa in the urine collected from each subject for 48 hours after drug administration. In mice each having received a single intraperitoneal dose of floctafenin (2 mg), the concentration of floctafenin declined by about 50 per cent in 15 minutes, and this decline was accompanied by a rise in the concentration of FFa that remained constant for 3 hours. The analgesic effect observed after administration of floctafenin to humans is likely to be mediated by its major metabolite, FFa. In these volunteers no free floctafenin was detected in the blood.

Adult↗