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At least 451 records · Page 25Linked to original sources
PubMed1971

Biosynthesis of the iron-transport compound enterochelin: mutants of Escherichia coli unable to synthesize 2,3-dihydroxybenzoate.

Mutants of Escherichia coli K-12 blocked in each of the three enzymatic reactions between chorismate and 2,3-dihydroxybenzoate, in the pathway leading to the iron-sequestering compound enterochelin, have been isolated and biochemically characterized. The three genes concerned (designated entA, entB and entC) have been shown to be clustered on the chromosome between purE and gal and to be located near minute 14 by cotransduction with the purE, lip, and fep genes. entA, entB, and entC were shown to be the structural genes for 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase, 2,3-dihydro-2,3-dihydroxybenzoate synthetase, and isochorismate synthetase, respectively.

Benzoates↗
PubMed2002

Kanosamine biosynthesis: a likely source of the aminoshikimate pathway's nitrogen atom.

The biosynthetic source of the nitrogen atom incorporated into the aminoshikimate pathway has remained a question for some time. 3-Amino-3-deoxy-D-fructose 6-phosphate has previously been demonstrated to be a precursor to 4-amino-3,4-dideoxy-D-arabino-heptulosonic acid 7-phosphate and 3-amino-5-hydroxybenzoic acid via the inferred intermediacy of 1-deoxy-1-imino-D-erythrose 4-phosphate in Amycolatopsis mediterranei cell-free extract. This investigation examines the possibility that the natural product kanosamine might be a precursor to 3-amino-3-deoxy-D-fructose 6-phosphate. Kanosamine 6-phosphate was synthesized by a chemoenzymatic route and incubated in A. mediterranei cell-free lysate along with D-ribose 5-phosphate and phosphoenolpyruvate. Formation of 4-amino-3,4-dideoxy-D-arabino-heptulosonic acid 7-phosphate and 3-amino-5-hydroxybenzoic acid was observed. Subsequent incubation in A. mediterranei cell-free lysate of glutamine and NAD with UDP-glucose resulted in the formation of kanosamine. The bioconversion of UDP-glucose into kanosamine along with the bioconversion of kanosamine 6-phosphate into 4-amino-3,4-dideoxy-D-arabino-heptulosonic acid 7-phosphate and 3-amino-5-hydroxybenzoic acid suggests that kanosamine biosynthesis is the source of the aminoshikimate pathway's nitrogen atom.

Actinomycetales↗
PubMed1971

Azaserine.

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Amino Acids↗
PubMed1969

Regulated enzymes of aromatic amino acid synthesis: control, isozymic nature, and aggregation in Bacillus subtilis and Bacillus licheniformis.

Several regulated enzymes involved in aromatic amino acid synthesis were studied in Bacillus subtilis and B. licheniformis with reference to organization and control mechanisms. B. subtilis has been previously shown (23) to have a single 3-deoxy-d-arabinoheptulosonate 7-phosphate (DAHP) synthetase but to have two isozymic forms of both chorismate mutase and shikimate kinase. Extracts of B. licheniformis chromatographed on diethylaminoethyl (DEAE) cellulose indicated a single DAHP synthetase and two isozymic forms of chorismate mutase, but only a single shikimate kinase activity. The evidence for isozymes has been supported by the inability to find strains mutant in these activities, although strains mutant for the other activities were readily obtained. DAHP synthetase, one of the isozymes of chorismate mutase, and one of the isozymes of shikimate kinase were found in a single complex in B. subtilis. No such complex could be detected in B. licheniformis. DAHP synthetase and shikimate kinase from B. subtilis were feedback-inhibited by chorismate and prephenate. DAHP synthetase from B. licheniformis was also feedback-inhibited by these two intermediates, but shikimate kinase was inhibited only by chorismate. When the cells were grown in limiting tyrosine, the DAHP synthetase, chorismate mutase, and shikimate kinase activities of B. subtilis were derepressed in parallel, but only DAHP synthetase and chorismate mutase were derepressible in B. licheniformis. Implications of the differences as well as the similarities between the control and the pattern of enzyme aggregation in the two related species of bacilli were discussed.

Bacillus↗
PubMedDate not supplied

Microbial synthesis of 3-dehydroshikimic acid: a comparative analysis of D-xylose, L-arabinose, and D-glucose carbon sources.

3-Dehydroshikimic acid is a hydroaromatic precursor to chemicals ranging from L-phenylalanine to adipic acid. The concentration and yield of 3-dehydroshikimic acid microbially synthesized from various carbon sources has been examined under fed-batch fermentor conditions. Examined carbon sources included D-xylose, L-arabinose, and D-glucose. A mixture consisting of a 3:3:2 molar ratio of glucose/xylose/arabinose was also evaluated as a carbon source to model the composition of pentose streams potentially resulting from the hydrolysis of corn fiber. Escherichia coli KL3/pKL4.79B, which overexpresses feedback-insensitive DAHP synthase, synthesizes higher concentrations and yields of 3-dehydroshikimic acid when either xylose, arabinose, or the glucose/xylose/arabinose mixture is used as a carbon source relative to when glucose alone is used as a carbon source. E. coli KL3/pKL4.124A, which overexpresses transketolase and feedback-insensitive DAHP synthase, synthesizes higher concentrations and yields of 3-dehydroshikimic acid when the glucose/xylose/arabinose mixture is used as the carbon source relative to when either xylose or glucose is used as a carbon source. Observed high-titer, high-yielding synthesis of 3-dehydroshikimic acid from the glucose/xylose/arabinose mixture carries significant ramifications relevant to the employment of corn fiber in the microbial synthesis of value-added chemicals.

Arabinose↗
PubMed2004

Synthesis of aminoshikimic acid.

5-amino-5-deoxyshikimic acid (aminoshikimic acid) was synthesized from glucose using recombinant Amycolatopsis mediterranei and also synthesized by a tandem, two-microbe route employing Bacillus pumilus and recombinant Escherichia coli.

Actinomycetales↗
PubMed2002

The structure and mechanism of the type II dehydroquinase from Streptomyces coelicolor.

The structure of the type II DHQase from Streptomyces coelicolor has been solved and refined to high resolution in complexes with a number of ligands, including dehydroshikimate and a rationally designed transition state analogue, 2,3-anhydro-quinic acid. These structures define the active site of the enzyme and the role of key amino acid residues and provide snap shots of the catalytic cycle. The resolution of the flexible lid domain (residues 21-31) shows that the invariant residues Arg23 and Tyr28 close over the active site cleft. The tyrosine acts as the base in the initial proton abstraction, and evidence is provided that the reaction proceeds via an enol intermediate. The active site of the structure of DHQase in complex with the transition state analog also includes molecules of tartrate and glycerol, which provide a basis for further inhibitor design.

Amino Acid Sequence↗
PubMed1995

Genetic aspects of aromatic amino acid biosynthesis in Lactococcus lactis.

Polymerase chain reaction (PCR) primers designed from a multiple alignment of predicted amino acid sequences from bacterial aroA genes were used to amplify a fragment of Lactococcus lactis DNA. An 8 kb fragment was then cloned from a lambda library and the DNA sequence of a 4.4 kb region determined. This region was found to contain the genes tyrA, aroA, aroK, and pheA, which are involved in aromatic amino acid biosynthesis and folate metabolism. TyrA has been shown to be secreted and AroK also has a signal sequence, suggesting that these proteins have a secondary function, possibly in the transport of amino acids. The aroA gene from L. lactis has been shown to complement an E. coli mutant strain deficient in this gene. The arrangement of genes involved in aromatic amino acid biosynthesis in L. lactis appears to differ from that in other organisms.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗
PubMed1996

4-Hydroxybutyryl-CoA dehydratase from Clostridium aminobutyricum: characterization of FAD and iron-sulfur clusters involved in an overall non-redox reaction.

4-Hydroxybutyryl-CoA dehydratase catalyzes the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA, which involves cleavage of an unactivated beta-C-H bond. The enzyme also catalyzes the apparently irreversible isomerization of vinylacetyl-CoA to crotonyl-CoA. Addition of crotonyl-CoA to the dehydratase, which contains FAD as well as non-heme iron and acid labile sulfur, led to a decrease of the flavin absorbance at 438 nm and an increase in the region from 500 to 800 nm. The protein-bound FAD was easily reduced to the semiquinone (redox equilibration within seconds) and only slowly to the hydroquinone (redox equilibration minutes to hours): the redox potentials were not unusual for flavoproteins (Eox/sq = -140 +/- 15 mV and Esq/red = -240 +/- 15 mV; pH 7.0, 25 degrees C). There was no equilibration of electrons between the flavin and the Fe-S cluster, which was difficult to reduce. After extensive photoreduction, an EPR signal indicative of a [4Fe-4S]+ cluster was detected (g-values: 2.037, 1.895, 1.844). Upon exposure to air at 0 degrees C, the enzyme lost dehydration activity completely within 40 min, but isomerase activity dropped to about 40% of the initial value and persisted for more than a day. The properties of the protein-bound FAD are consistent with a mechanism involving transient one-electron oxidation of the substrate to activate the the beta-C-H bond. The putative [4Fe-4S]2+ cluster could serve a structural role and/or as Lewis acid facilitating the leaving of the hydroxyl group.

Acetyl Coenzyme A↗