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At least 307 records · Page 17Linked to original sources
PubMed1978

Genetical and biochemical characterization of QA-3 mutants and revertants in the QA gene cluster of Neurospora crassa.

The qa-3 gene, one of the four genes in the qa gene cluster, encodes quinate (shikimate) dehydrogenase (quinate: NAD oxidoreductase, ER 1.1.1.24), the first enzyme in the inducible quinic acid catabolic pathway in Neurospora crassa. Genetic analyses have localized 26 qa-3 mutants at 11 sites on the aq-3 genetic map on the basis of prototroph frequencies. Certain mutants, e.g., 336-3-10 and 336-3-3, are located at opposite ends of the qa-3 gene. Data from four-point crosses (qa-1s mutant 124 X five different qa-3 mutants in triple mutants qa-3, qa-4, qa-2) indicate the following orientation of the qa-3 gene within the qa cluster; qa-1, qa-3 mutant 336-3-10 ("left" end) qa-3 mutant 336-3-3 ("right" end), qa-4, qa-2. Ultraviolet-induced revertants have been obtained from 14 of the qa-3 mutants. The revertable mutants fall into two major classes: those that revert by changes either at the same site or at a second site within the qa-3 gene, and those that revert by unlinked suppressor mutations. The intragenic revertants can be further distinguished by quantative and/or qualitative differences in their quinate dehydrogenase activities. Some revertants with activities either equivalent to or less than wild type produce a thermostable enzyme, and others an enzyme which is thermolabile in vitro at 35 degrees. A concentration of quinic acid or shikimic acid as low as 50 micron protects the enzyme markedly from heat inactivation. The genetic organization and the orientation of the qa-3 gene are discussed with respect to its direction of transcription and to the possible localization of a promoter (initiator) region(s) within the qa gene cluster.

Alcohol Oxidoreductases↗
PubMed1979

Aromatic amino acid biosynthesis: regulation of shikimate kinase in Escherichia coli K-12.

Starvation of cells of Escherichia coli K-12 for the aromatic amino acids results in an increased rate of synthesis of shikimate kinase activity. The two controlling amino acids are tyrosine and tryptophan, and starvation for both results in derepression. The product of the regulator gene tyrR also participates in this control, and shikimate kinase synthesis was depressed in tyrR mutants. Chromatography of cell extracts on diethylaminoethyl-Sephadex allowed partial separation of two shikimate kinase enzymes and demonstrated that only one of these subject to specific repression control involving tyrR. By contrast, chromatography of cell extracts with G-75 or G-200 columns revealed a singl-molecular-weight species of shikimate kinase activity with an apparent molecular weight of 20,000. The levels of shikimate kinase in a series of partial diploid strains indicated that aroL, the structural gene for the tyrR-controlled shikimate kinase enzyme, is located on the E. coli chromosome between the structural genes proC and purE. By means of localized mutagenesis, an aroL mutant of E. coli was isolated. The mutant was an aromatic prototroph and, by the criterion of column chromatography, appeared to have only a single functional species of shikimate kinase enzyme.

Amino Acids↗
PubMed2003

Crystal structure of shikimate 5-dehydrogenase (SDH) bound to NADP: insights into function and evolution.

The crystal structure of Methanococcus jannaschii shikimate 5-dehydrogenase (MjSDH) bound to the cofactor nicotinamide adenine dinucleotide phosphate (NADP) has been determined at 2.35 A resolution. Shikimate 5-dehydrogenase (SDH) is responsible for NADP-dependent catalysis of the fourth step in shikimate biosynthesis, which is essential for aromatic amino acid metabolism in bacteria, microbial eukaryotes, and plants. The structure of MjSDH is a compact alpha/beta sandwich with two distinct domains, responsible for binding substrate and the NADP cofactor, respectively. A phylogenetically conserved deep cleft on the protein surface corresponds to the enzyme active site. The structure reveals a topologically new domain fold within the N-terminal segment of the polypeptide chain, which binds substrate and supports dimerization. Insights gained from homology modeling and sequence/structure comparisons suggest that the SDHs represent a unique class of dehydrogenases. The structure provides a framework for further investigation to discover and develop novel inhibitors targeting this essential enzyme.

Alcohol Oxidoreductases↗
PubMed1969

Organization of enzymes in the common aromatic synthetic pathway: evidence for aggregation in fungi.

Centrifugation in sucrose density gradients of partially purified extracts from six species of fungi, i.e., Rhizopus stolonifer, Phycomyces nitens, Absidia glauca (Phycomycetes), Aspergillus nidulans (Ascomycetes), Coprinus lagopus, and Ustilago maydis (Basidiomycetes), indicate that the five enzymes catalyzing steps two to six in the prechorismic acid part of the polyaromatic synthetic pathway sediment together. The sedimentation coefficients for these enzymes are very similar in the six species and are comparable to those previously observed for the multienzyme complexes (arom aggregates) of Neurospora crassa and Saccharomyces cerevisiae. These results are interpreted as indicating the presence in each of these fungi of arom aggregates, presumably encoded by arom gene clusters similar to those in N. crassa and S. cerevisiae. Evidence has also been obtained for the presence in two species (A. nidulans and U. maydis) and the absence in the other four species of a second dehydroquinase isozyme which is distinguishable from the synthetic activity on the basis of both thermostability tests and S values. This second dehydroquinase, which is apparently involved in the catabolism of quinic acid via a pathway similar to that in N. crassa, is inducible in A. nidulans (as it is in N. crassa), but constitutive in U. maydis. These comparative findings are discussed in relation to the organization, evolution, and possible functional relationships of synthetic and catabolic aromatic pathways in fungi.

Alcohol Oxidoreductases↗
PubMed2002

Study of the organic acids composition of quince (Cydonia oblonga Miller) fruit and jam.

The organic acids present in several samples of quince fruit (pulp and peel) and quince jam (homemade and industrially manufactured) were analyzed by HPLC. The sample preparation was simple, involving only extraction with methanol (40 degrees C) and filtration through a Sep-pack C18 cartridge. The chromatographic separation was achieved using an ion exclusion column, Nucleogel Ion 300 OA (300 x 7.7 mm), in conjunction with a column heating device at 30 degrees C. An isocratic elution with H(2)SO(4) 0.01 N as the mobile phase, with a flow rate of 0.1 mL/min, and UV detection at 214 nm were used. These analyses showed that all samples presented a similar profile composed of at least six identified organic acids: citric, ascorbic, malic, quinic, shikimic, and fumaric acids. Several samples also contained oxalic acid. This study suggests that the organic acids levels and ratios may be useful for the determination of percent fruit content of quince jams. The citric acid value can also be used in the differentiation of the type of manufacture of the commercial quince jams (homemade or industrially manufactured).

Ascorbic Acid↗
PubMed1975

Omega-cyclohexyl fatty acids in acidophilic thermophilic bacteria. Studies on their presence, structure, and biosynthesis using precursors labeled with stable isotopes and radioisotopes.

Omega-Cyclohexyl undecanoic acid and omega-cyclohexyl tridecanoic acid were found in 10 strains of acido-thermophilic bacteria isolated from different Japanese hot springs. These unusual fatty acids were found in the esterified form in glyceride type complex lipids and constituted 74 to 93% of the total fatty acids in the bacteria. The fatty acids other than omega-cyclohexyl fatty acids found were 14-methyl hexadecanoic acid (3 to 15%) and 15-methyl hexadecanoic acid (1 to 6%), and trace amounts of straight chain and methyl-branched tetra- and penta-decanoic acids. Biosynthesis of omega-cyclohexyl fatty acids increased with increase in the concentration of glucose in the culture medium. The metabolism of omega-cyclohexyl fatty acids was studied using deuterium-labeled precursors by mass fragmentation analysis. The deuterium of [2-D]glucose was specifically incorporated into position 2 of the cyclohexyl ring of the fatty acids, indicating that the ring was synthesized from the glucose molecule. Radioactivity was efficiently incorporated into the omega-cyclohexyl fatty acids from labeled glucose, shikimate, and cyclohexyl carboxylate. These findings indicate that omega-cyclohexyl fatty acids are synthesized with glucose through shikimic acid and probably cyclohexyl carboxylyl-CoA derivative as the intermediates.

Acetates↗