PubMed Health⌕ Search

Biomedical subjects

F Gibson

Publications and source records attributed to F Gibson.

At least 127 records · Page 7Linked to original sources
PubMed1972

Anthranilate synthase-anthranilate 5-phosphoribosyl 1-pyrophosphate phosphoribosyltransferase from Aerobacter aerogenes.

1. Anthranilate synthase and phosphoribosyltransferase from Aerobacter aerogenes purify simultaneously and sediment together on sucrose gradients, showing that they occur as an enzyme aggregate. Both activities of the intact aggregate are subject to inhibition by tryptophan. 2. By using appropriate auxotrophic mutants it was shown that an intact active enzyme aggregate is formed when the components come from separate mutant strains. An intact active aggregate can also be formed when one component is from Escherichia coli and the other from A. aerogenes. 3. Phosphoribosyltransferase of A. aerogenes is active when not in an aggregate with anthranilate synthase, but is not subject to tryptophan inhibition, indicating that the inhibitor site is on the anthranilate synthase component. 4. Anthranilate synthase can be active and sensitive to tryptophan inhibition when complexed with an inactive phosphoribosyltransferase. 5. Kinetic studies on the anthranilate synthase activity show that tryptophan is a competitive inhibitor with respect to chorismate and a non-competitive inhibitor with respect to either glutamine or NH(4) (+) ions. This is consistent with a sequential mechanism of the ordered type in which chorismate is the first reactant.

Binding Sites↗
PubMed1972

Mutants of Escherichia coli K-12 blocked in the final reaction of ubiquinone biosynthesis: characterization and genetic analysis.

The ubiquinone precursor 2-octaprenyl-3-methyl-5-hydroxy-6-methoxy-1, 4-benzoquinone was isolated from two ubiquinone-deficient mutants of Escherichia coli and identified by nuclear magnetic resonance and mass spectrometry. The results of genetic analysis of the mutants indicate that each mutant carries a mutation in a gene designated ubiG which was located, by cotransduction with the nalA and glpT genes, at minute 42 on the E. coli chromosome.

Cell-Free System↗
PubMed1972

Function of ubiquinone in Escherichia coli: a mutant strain forming a low level of ubiquinone.

A ubiquinone-deficient mutant of Escherichia coli K-12 forming 20% of the normal amount of ubiquinone was compared with a normal strain. This lowered concentration of ubiquinone is still four times the concentration of cytochrome b(1). The mutant strain grew more slowly than the normal strain on a minimal medium with glucose as sole source of carbon and gave a lower aerobic growth yield than the normal strain. The reduced nicotinamide adenine dinucleotide (NADH) oxidase rate in membranes from the mutant strain was 40% of the oxidase rate in membranes from the normal strain, and the percentage reduction of cytochrome b(1) in the aerobic steady state, with NADH as substrate, was increased in membranes from the mutant strain. It is concluded that ubiquinone is required for maximum oxidase activity at the relatively high concentration (27 times that of cytochrome b(1)) found in normal cells. The results are discussed in relation to a scheme previously advanced for ubiquinone function in E. coli.

Aerobiosis↗
PubMed1972

Biochemical and genetic studies on ubiquinone biosynthesis in Escherichia coli K-12:4-hydroxybenzoate octaprenyltransferase.

Three ubiquinone-deficient mutants of Escherichia coli unable to convert 4-hydroxybenzoate into 3-octaprenyl-4-hydroxybenzoate were isolated and examined. The results of genetic analysis suggest that each of the mutants carries a mutation in a gene designated ubiA which can be represented at minute 79 on the E. coli chromosome map. The conversion of 4-hydroxybenzoate into 3-octaprenyl-4-hydroxybenzoate, catalyzed by 4-hydroxybenzoate octaprenyltransferase, was studied with a strain of E. coli that is blocked in the common pathway of aromatic biosynthesis and consequently accumulates the precursor of the side chain of ubiquinone. Both the side-chain precursor and 4-hydroxybenzoate octaprenyltransferase were shown to be membrane-bound. The enzyme required Mg(2+) for optimal activity. The ubiA(-) mutants were found to lack 4-hydroxybenozate octaprenyltransferase activity, which suggested that the ubiA gene is the structural gene coding for this enzyme.

Alkyl and Aryl Transferases↗
PubMed1972

Enterochelin system of iron transport in Escherichia coli: mutations affecting ferric-enterochelin esterase.

Three mutant strains of Escherichia coli have been isolated which are lacking ferric-enterochelin esterase activity. This enzyme catalyzes the hydrolysis of the enterochelin moiety of ferric-enterochelin to yield ultimately three molecules of N-2,3-dihydroxybenzoylserine. The mutants (designated fes(-)) were shown to be unaffected in enterochelin biosynthesis, capable of enterochelin-mediated iron uptake, and able to utilize ferric-dihydroxybenzoylserine complexes normally. When grown under iron-deficient conditions, however, they showed an absolute requirement for added iron or citrate, a phenotype characteristic of mutants defective in some part of the enterochelin system of iron uptake. These results support the theory that iron, taken up by the cell as ferric-enterochelin is only available for general cell metabolism after hydrolysis of the ligand by enterochelin esterase. The three fes(-) strains were shown to be affected in the B component of enterochelin esterase. The fesB gene which is probably the structural gene coding for component B of the esterase, was shown to be located at about minute 14 on the E. coli chromosome together with seven other genes involved in the enterochelin system of iron transport.

Benzoates↗
PubMed1971

Oxidative phosphorylation in Escherichia coli K12. Mutations affecting magnesium ion- or calcium ion-stimulated adenosine triphosphatase.

1. Two mutants of Escherichia coli K 12 were isolated which, although able to grow on glucose, are unable to grow with succinate or d-lactate as the sole source of carbon. 2. Genetic mapping of these mutants showed that they both contain a mutation in a gene (designated uncA) mapping at about minute 73.5 on the E. coli chromosome. 3. The uncA(-) alleles were transferred by bacteriophage-mediated transduction into another strain of E. coli and the transductants compared with the parent strain to determine the nature of the biochemical lesion in the mutants. 4. The mutants gave low aerobic growth yields when grown on limiting concentrations of glucose, but oxidase activities in membranes from both the mutants and the normal strain were similar. 5. Measurement of P/O ratios with d-lactate as substrate indicated that a mutation in the uncA gene causes uncoupling of phosphorylation associated with electron transport. 6. Determination of the Mg(2+),Ca(2+)-stimulated adenosine triphosphatase activities in the mutant and normal strains indicated that the uncA gene is probably the structural gene for Mg(2+),Ca(2+)-stimulated adenosine triphosphatase. 7. Mg(2+),Ca(2+)-stimulated adenosine triphosphatase therefore appears to be essential for oxidative phosphorylation in E. coli.

Adenosine Triphosphatases↗
PubMed1971

The energy-linked transhydrogenase reaction in respiratory mutants of Escherichia coli K12.

1. Energy-linked and non-energy-linked transhydrogenase activities were assayed in membrane preparations from normal Escherichia coli K 12 and from various mutant strains. 2. The energy-linked transhydrogenase, which uses ATP as energy source, was dependent for activity on the presence of a functional Mg(2+)+Ca(2+)-stimulated adenosine triphosphatase. 3. Neither of the quinones formed by E. coli, namely ubiquinone-8 and menaquinone-8, was required for normal ATP-dependent energy-linked transhydrogenase activity. 4. The energy-linked transhydrogenase was inhibited by piericidin A at a site unrelated to the sites of inhibition of the electron-transport chain by piericidin A.

Adenosine Triphosphatases↗
PubMed1971

Characterization and genetic analysis of mutant strains of Escherichia coli K-12 accumulating the biquinone precursors 2-octaprenyl-6-methoxy-1,4-benzoquinone and 2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone.

The ubiquinone precursors, 2-octaprenyl-6-methoxy-1,4-benzoquinone and 2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone, were isolated from ubiquinone-deficient mutants of Escherichia coli and identified by nuclear magnetic resonance and mass spectrometry. Mutants accumulating 2-octaprenyl-6-methoxy-1,4-benzoquinone and 2-octaprenyl-3-methyl-6-methoxy-1,4-benzoquinone were shown to carry mutations in genes designated ubiE and ubiF, respectively. The ubiE gene was shown to be cotransducible with metE (minute 75) and close to two other genes concerned with ubiquinone biosynthesis. The ubiF gene was located close to minute 16 by cotransduction with the lip, gltA, and entA genes.

Benzene↗
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↗
PubMed1971

Location of three genes concerned with the conversion of 2,3-dihydroxybenzoate into enterochelin in Escherichia coli K-12.

Mutants of Escherichia coli K-12 unable to synthesize the iron-sequestering compound, enterochelin, from 2,3-dihydroxybenzoate have been isolated and divided into three classes on the basis of tests for enzymatic complementation. The genes affected (designated entD, entE, and entF) have been mapped by cotransduction and are located at about minute 14 on the E. coli genome. They were found to be closely linked to other genes (entA, entB, and entC) concerned with enterochelin biosynthesis and a gene (fep) concerned with the uptake of the iron-enterochelin complex. No detectable diffusible intermediate in the formation of enterochelin from 2,3-dihydroxybenzoate was formed by cell extracts of mutants carrying mutations in the entD, entE, or entF genes.

Benzoates↗