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At least 1,153 records · Page 64Linked to original sources
PubMed2000

Synthesis, spectral characterization, and structural studies of 2-aminobenzoate complexes of divalent alkaline earth metal ions: X-ray crystal structures of [Ca(2-aba)2(OH2)3]infinity, [[Sr(2-aba)2(OH2)2].H2O]infinity, and [Ba(2-aba)2(OH2)]infinity (2-abaH = 2-NH2C6H4COOH).

Reactions of alkaline earth metal chlorides with 2-aminobenzoic acid (2-abaH) have been investigated. The treatment of MCl2.nH2O (M = Mg, Ca, Sr or Ba) with 2-abaH in a 1:2 ratio in a MeOH/H2O/NH3 mixture leads to the formation of anthranilate complexes [Mg(2-aba)2] (1), [Ca(2-aba)2(OH2)3]infinity (2), [[Sr(2-aba)2(OH2)2].H2O)]infinity (3), and [Ba(2-aba)2(OH2)]infinity (4) respectively. Alternatively, these products can also be obtained starting from the corresponding metal acetates. Anthranilate complexes 1-4 have been characterized with the aid of elemental analysis, pH measurements, thermal analysis, and infrared, ultraviolet, and NMR (1H and 13C) spectroscopic studies. All the products are found to be thermally very stable and do not melt on heating to 250 degrees C. Thermal studies of complexes 2-4, however, indicate the loss of coordinated and lattice water molecules below 200 degrees C. In the case of the magnesium complex, the analytical and thermogravimetric studies indicate the absence of any coordinated or uncoordinated water molecules. Further, the solid-state structures of metal anthranilates 2-4 have been established by single-crystal X-ray diffraction studies. While the calcium ions in 2 are heptacoordinated, the strontium and barium ions in 3 and 4 reveal a coordination number of 9 apart from an additional weak metal-metal interaction along the polymeric chains. The carboxylate groups show different chelating and bridging modes of coordination behavior in the three complexes. Interestingly, apart from the carboxylate functionality, the amino group also binds to the metal centers in the case of strontium and barium complexes 3 and 4. However, the coordination sphere of 2 contains only O donors. All three compounds form polymeric networks in the solid state with the aid of different coordinating capabilities of the carboxylate anions and O-H...O and N-H...O hydrogen bonding interactions.

Journal Article↗
PubMed1973

Tryptophan biosynthetic enzymes of Staphylococcus aureus.

Tryptophan biosynthetic enzymes were assayed in various tryptophan mutants of Staphylococcus aureus strain 655 and the wild-type parent. All mutants, except trpB mutants, lacked only the activity corresponding to the particular biosynthetic block, as suggested previously by analysis of accumulated intermediates and auxonography. Tryptophan synthetase A was not detected in extracts of either trpA or trpB mutants but appeared normal in other mutants. Mutants in certain other classes exhibited partial loss of another particular tryptophan enzyme activity. Tryptophan synthetase B activity was not detected in cell extract preparations but was detected in whole cells. The original map order proposed for the S. aureus tryptophan gene cluster was clarified by the definition of trpD (phosphoribosyl transferase(-)) and trpF (phosphoribosyl anthranilate isomerase(-)) mutants. These mutants were previously unresolved and designated as trp(DF) mutants (anthranilate accumulators). Phosphoribosyl anthranilate isomerase and indole-3-glycerol phosphate synthetase enzymes were separable by molecular sieve chromatography, suggesting that these functions are coded by separate loci. Molecular sieve chromatography failed to reveal aggregates involving anthranilate synthetase, phosphoribosyl transferase, phosphoribosyl anthranilate isomerase, and indole-3-glycerol phosphate synthetase, and this procedure provided an estimate of the molecular weights of these enzymes. Tryptophan was shown to repress synthesis of all six tryptophan biosynthetic enzymes, and derepression of all six activities was incident upon tryptophan starvation. Tryptophan inhibited the activity of anthranilate synthetase, the first enzyme of the pathway.

Carboxy-Lyases↗
PubMed1980

Mechanism of inactivation of glutamine amidotransferases by the antitumor drug L-(alpha S, 5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125).

L-(alphaS, 5S)-alpha-Amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT-125), an antitumor drug isolated from Streptomyces sviceus, is an active site-directed affinity analog of glutamine. It selectively inactivates the glutamine-dependent activities of two bacterial glutamine amidotransferases, anthranilate synthase and glutamate synthase. A reversible noncovalent complex is formed prior to irreversible enzyme modification. Inactivation of anthranilate synthase results from incorporation of approximately 1 eq of AT-125/enzyme protomer. Active site cysteine-83 in Serratia marcescens anthranilate synthase Component II is the residue alkylated by AT-125. Anthranilate synthase is rapidly inactivated by AT-125 IN S. marcescens cells. In vivo inactivation is by the same mechanism as in vitro.

Anthranilate Synthase↗
PubMed2002

The pab1 gene of Coprinus cinereus encodes a bifunctional protein for para-aminobenzoic acid (PABA) synthesis: implications for the evolution of fused PABA synthases.

The pab1 gene of the basidiomycete Coprinus cinereus encodes PABA synthase, necessary for para-aminobenzoic acid production. The C. cinereus protein is bifunctional with an N-terminal glutamine amidotransferase domain and a C-terminal chorismate amination domain. In most bacteria, these two functions are encoded in separate genes (e.g., pabA and pabB of E. coli). Fused PABA synthases have so far been detected in actinomycetes, Plasmodium falciparum, fungi and Arabidopsis thaliana. Phylogenetic analysis shows that the fused PAB sequences form a tight group that also includes uncharacterized PabB homologues from several bacteria. Unfused bacterial PabA proteins group with the glutamine amidotransferase subunits of bacterial anthranilate synthases, independent of organismal systematics, indicating a complex and perhaps independent evolutionary origin. In contrast, unfused PabB group and fused PabA/B proteins form a monophyletic group on a branch separate from the chorismate amination subunits of anthranilate synthases, probably reflecting a need for recognition of different positions in the common substrate chorismate.

4-Aminobenzoic Acid↗
PubMed1976

Naturally occurring sites within the Shigella dysenteriae tryptophan operon severely limit tryptophan biosynthesis.

We investigated the structural, functional, and regulatory properties of the Shigella dysenteriae tryptophan (trp.) operon in transduction hybrids in which the cysB-trp-region of Escherichia coli is replaced by the corresponding region from S. dysenteriae. Tryptophan biosynthesis was largely blocked in the hybrids, although the order of the structural genes was identical with that of E. coli. Nutritional tests and enzyme assays revealed that the hybrids produced a defective anthranilate synthetase (ASase). Deletion mapping identified two distinct sites in trpE, each of which was partially responsible for the instability and low activity of ASase. We also discovered a pleiotropic site trpP (S) that maps outside the structural gene region and is closely linked to the S. dysenteriae trp operator. trpP (S) reduced the rate of trp messenger ribonucleic acid synthesis, and consequently trp enzyme levels, 10-fold relative to wild-type E. coli. In recombinants in which the structural genes of E coli were under the control of the S. dysenteriae promoter, enzyme levels were also reduced 10-fold. In some fast-growing revertants of the original hybrids, the rates of trp messenger ribonucleic acid synthesis and levels of tryptophan synthetase were restored to values characteristic of wild-type E.coli. Thus, the Trp auxotrophy associated with the S dysenteriae trp operon derives from the combination of a defective ASase and decreased expression of the entire operon imposed by trpP (S).

Anthranilate Phosphoribosyltransferase↗
PubMed2005

The biosynthesis and regulation of biosynthesis of Concord grape fruit esters, including 'foxy' methylanthranilate.

The biosynthesis of methyl anthranilate, the volatile compound responsible for the distinctive 'foxy' aroma and flavor of the Washington Concord grape (Vitis labrusca), involves an alcohol acyltransferase that catalyzes the formation of methyl anthranilate from anthraniloyl-coenzyme A (CoA) and methanol. Although methanol is a poor substrate in comparison with the co-substrate, high levels of this acyltransferase (0.5% of the total protein) combined with relatively high levels of this alcohol make this reaction possible in grapes. This 449 amino acid protein belongs to the BAHD family of acyltransferases, having 58% identity with the benzoyl CoA:benzyl alcohol benzoyl transferase from Clarkia. Both native and recombinant enzymes can use a broad range of acyl-CoAs and alcohols as substrates. The ability of Concord grape alcohol acyltransferase to accept a range of different CoA esters and alcohols suggests this to be a versatile ester-forming enzyme, similar to those of other fruits that than can produce a range of fruit esters based on the supply of appropriate substrates. Expression is coordinately regulated, with transcript, protein and enzyme activities coinciding with the accumulation of methyl anthranilate that occurs after the initiation of berry ripening. The majority of acyltransferase protein in grape tissues is localized to the outer fruit mesocarp, a result consistent with the fact that methyl anthranilate is released to the external environment throughout the ripening process. Wine grapes (Vitis vinifera) that accumulate neither anthranilate nor methyl anthranilate do not express this enzyme activity nor do they accumulate this protein.

Base Sequence↗
PubMed1966

Control of aromatic acid biosynthesis in Bacillus subtilis: sequenial feedback inhibition.

Nester, E. W. (University of Washington, Seattle), and R. A. Jensen. Control of aromatic acid biosynthesis in Bacillus subtilis: sequential feedback inhibition. J. Bacteriol. 91:1594-1598. 1966.-The three major end products of aromatic acid synthesis, tyrosine, phenylalanine, and tryptophan, were tested for their ability to inhibit the first enzymes of the three terminal branches of the pathway as well as the enzyme common to both tyrosine and phenylalanine synthesis. Tyrosine inhibits the activity of prephenate dehydrogenase and also prephenate dehydratase to a limited extent. Phenylalanine inhibits the activity of prephenate dehydratase and, at much higher concentrations, prephenate dehydrogenase. Tryptophan inhibits the activity of anthranilate synthetase and, to some extent, prephenate dehydrogenase and prephenate dehydratase. Chorismate mutase is not inhibited by either 1 mm tyrosine or 1 mm phenylalanine when these are present singly or together in the reaction mixture. The significance of the feedback control of the terminal branches to the feedback control of that part of the pathway common to the synthesis of all three amino acids is discussed.

Bacillus subtilis↗
PubMed1985

Methods for in vitro percutaneous absorption studies IV: The flow-through diffusion cell.

A flow-through diffusion cell system for percutaneous absorption studies has been developed. The results of initial studies with a limited number of compounds are reported. The cells were constructed from Teflon and contained a glass window in the bottom for viewing the receptor contents. A flow rate of at least 5 mL/h is required through the receptor (volume, 0.4 mL) for accurate results. The skin permeation of water, cortisone, and benzoic acid was determined in the flow-through cell and a standard static-diffusion cell. The absorption profiles and quantitative values obtained were similar for the two types of cells. The permeation of cortisone and benzoic acid applied in a petrolatum vehicle was determined in vivo in rats and with rat skin in the flow-through and static-diffusion cells. Good agreement was obtained between the results of the in vivo and in vitro procedures. The percutaneous absorption of a hydrophobic compound [3-phenyl-2-propenyl 2-aminobenzoate (cinnamyl anthranilate)] was enhanced with normal saline receptor solution in the flow-through cell when compared with results in the static cell. Maximum in vitro absorption was obtained with either cell using a 6% solution in water of the nonionic surfactant polyethylene glycol 20 oleyl ether (PEG-20 oleyl ether).

Animals↗
PubMed2000

Decay of mutualistic potential in aphid endosymbionts through silencing of biosynthetic loci: Buchnera of Diuraphis.

Buchnera, the primary bacterial endosymbiont of aphids, is known to provision essential amino acids lacking in the hosts' diet of plant sap. The recent discovery of silenced copies of genes for tryptophan biosynthesis (trpEG) in certain Buchnera lineages suggests a decay in symbiotic functions in some aphid species. However, neither the distribution of pseudogenes among lineages nor the impact of this gene silencing on amino-acid availability in hosts has been assessed. In Buchnera of the aphid Diuraphis noxia, tandem repeats of these pseudogenes have persisted in diverse lineages, and thpEG pseudogenes have originated at least twice within this aphid genus. Measures of amino-acid concentrations in Diuraphis species have shown that the presence of the pseudogene is associated with a decreased availability of tryptophan, indicating that gene silencing decreases nutrient provisioning by symbionts. In Buchnera of Diuraphis, rates of nonsynonymous substitutions are elevated in functional trpE copies, supporting the hypothesis that pseudogene origin and persistence reflect a reduced selection for symbiont biosynthetic contributions. The parallel evolution of trpEG pseudogenes in Buchnera of Diuraphis and certain other aphid hosts suggests that either selection at the host level is not effective or that fitness in these aphids is not limited by tryptophan availability.

Animals↗
PubMed1983

Tryptophan auxotrophs of Rhizobium japonicum.

Eleven tryptophan-requiring mutants of Rhizobium japonicum I-110 ARS were isolated after nitrous acid mutagenesis and fell into five groups based on characterization by supplementation with intermediates and enzyme assays.

Anthranilate Phosphoribosyltransferase↗
PubMed2000

Cross-talk and ammonia channeling between active centers in the unexpected domain arrangement of glutamate synthase.

INTRODUCTION: The complex iron-sulfur flavoprotein glutamate synthase catalyses the reductive synthesis of L-glutamate from 2-oxoglutarate and L-glutamine, a reaction in the plant and bacterial pathway for ammonia assimilation. The enzyme functions through three distinct active centers carrying out L-glutamine hydrolysis, conversion of 2-oxoglutarate into L-glutamate, and electron uptake from an electron donor. RESULTS: The 3.0 A crystal structure of the dimeric 324 kDa core protein of a bacterial glutamate synthase was solved by the MAD method, using the very weak anomalous signal of the two 3Fe-4S clusters present in the asymmetric unit. The 1,472 amino acids of the monomer fold into a four-domain architecture. The two catalytic domains have canonical Ntn-amidotransferase and FMN binding (beta/alpha)8 barrel folds, respectively. The other two domains have an unusual "cut (beta/alpha)8 barrel" topology and an unexpected novel beta-helix structure. Channeling of the ammonia intermediate is brought about by an internal tunnel of 31 A length, which runs from the site of L-glutamine hydrolysis to the site of L-glutamate synthesis. CONCLUSIONS: The outstanding property of glutamate synthase is the ability to coordinate the activity of its various functional sites to avoid wasteful consumption of L-glutamine. The structure reveals two polypeptide segments that connect the catalytic centers and embed the ammonia tunnel, thus being ideally suited to function in interdomain signaling. Depending on the enzyme redox and ligation states, these signal-transducing elements may affect the active site geometry and control ammonia diffusion through a gating mechanism.

Ammonia↗
PubMed1990

Molecular cloning, nucleotide sequence, and promoter structure of the Acinetobacter calcoaceticus trpFB operon.

The trpFB operon from Acinetobacter calcoaceticus encoding the phosphoribosyl anthranilate isomerase and the beta-subunit of tryptophan synthase has been cloned by complementation of a trpB mutation in A. calcoaceticus, identified by deletion analysis, and sequenced. It encodes potential polypeptides of 214 amino acids with a calculated molecular weight of 23,008 (TrpF) and 403 amino acids with a molecular weight of 44,296 (TrpB). The encoded TrpB sequence shows striking homologies to those from other bacteria, ranging from 47% amino acids identity with the Brevibacterium lactofermentum protein and 64% identity with the Caulobacter crescentus protein. The encoded TrpF sequence, on the other hand, is much less homologous to the ones from other species, ranging between 27% identity with the Bacillus subtilis enzyme and 36% identity with the C. crescentus enzyme. The homologies of both polypeptides are evenly distributed over the entire sequences. The codon usage shows the strong preference for A and T in the third positions typical for A. calcoaceticus genes. The trpFB operon appears to be unlinked to trpA. The trpFB promoter has been determined by primer extension analysis of RNA synthesized from the chromosomally and plasmid-encoded trpFB operons. The starting nucleotides are identical in both cases and define the first promoter from A. calcoaceticus. Potential regulatory features are implied by a palindromic element overlapping the -35 consensus box of the promoter.

Acinetobacter↗
PubMed1993

Overproduction of indole acetic acid in Azospirillum lipoferum using the Escherichia coli trp operon.

A recombinant plasmid carrying the trp operon from Escherichia coli, which synthesizes tryptophan from chorismate, was constructed by using a broad host range plasmid vector pRK290; a mutant trp plasmid for tryptophan overproduction was then selected. The physiological, biochemical, and genetic properties of the Azospirillum lipoferum KY6, a potential nitrogen fixer of rice, harbouring the recombinant trp plasmid pMJC1 and its mutant pMJC101, were compared with those of the wild-type bacteria. Anthranilate synthetase is known to be the trpE gene product which plays a key role in the regulatory step in the feedback control of tryptophan biosynthesis. The enzyme activity of the Azospirillum lipoferum KY6 carrying pMJC1 or pMJC101 was respectively 7- and 30-fold higher than that of the wild type in the presence of 10(-4)M tryptophan. As expected, the amount of tryptophan biosynthesis in A. lipoferum KY6 (pMJC101) was increased approximately 100-fold as compared with the wild type, which led to overproduction of indole acetic acid even without addition of exogenous tryptophan. Moreover, the recombinant trp plasmid was fairly stable in A. lipoferum KY6 host, showing only 25% loss of the plasmid itself or the trp insert after 40 generations.

Azospirillum↗