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  • Regulation  (27)
  • 1985-1989  (27)
  • 1
    ISSN: 1432-072X
    Keywords: Nitrogenase ; Nitrogen fixation ; Regulation ; Photosynthetic bacteria ; Chromatium ; Ammonia switch off
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogenase in Chromatium vinosum was rapidly, but reversibly inhibited by NH 4 + . Activity of the Fe protin component of nitrogenase required both Mn2+ and activating enzyme. Activating enzyme from Rhodospirillum rubrum could replace Chromatium chromatophores in activating the Chromatium Fe protein, and conversely, a protein fraction prepared from Chromatium chromatophores was effective in activating R. rubrum Fe protein. Inactive Chromatium Fe protein contained a peptide covalently modified by a phosphate-containing molecule, which migrated the same in SDS-polyacrylamide gels as the modified subunit of R. rubrum Fe protein. In sum, these observations suggest that Chromatium nitrogenase activity is regulated by a covalent modification of the Fe protein in a manner similar to that of R. rubrum.
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  • 2
    ISSN: 1432-072X
    Keywords: Restricted methylotroph ; RuMP pathway ; Growth on methanol and glucose ; Methanol dehydrogenase ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A restricted facultative methylotrophic RuMP type bacterium that can only utilize methanol and glucose has been found to possess a higher specific activity of methanol dehydrogenase during growth on glucose than during growth on methanol. The increased level of methanol dehydrogenase activity in glucose grown cells was the result of overproduction of the enzyme. In methanol grown cells 8% of the soluble protein consisted of methanol dehydrogenase, whereas in glucose grown cells the proportion amounted to 25%. The type of methanol dehydrogenase produced by this methylotroph could be separated from the crude extract and purified close to homogeneity in a one step procedure using cationic ion exchange chromatography. The enzyme is constitutive, and its level is determined by the growth rate.
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  • 3
    ISSN: 1432-072X
    Keywords: cAMP ; Isoleucyl-tRNA synthetase ; Regulation ; Gene ; Escherichia coli ; Expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The ability of cAMP to inhibit isoleucyl-tRNA synthetase (IRS) formation has been demonstrated in wild type K-12 Escherichia coli and two adenyl-cyclase (cya) mutants. cAMP appeared not to have any effect on either the valyl- or arginyl-tRNA synthetase (VRS and ARS respectively). Addition of cAMP led to a reduction in rate of IRS synthesis but not VRS or ARS. Furthermore, derepression of IRS and VRS by isoleucine limitation was completely prevented by cAMP.
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  • 4
    ISSN: 1432-072X
    Keywords: Arthrobacter P1 ; Methylamine ; Methylotrophy ; Regulation ; RuMP cycle of formaldehyde fixation ; Mutants ; Amine oxidase ; Hexulose phosphate synthase ; Formaldehyde dehydrogenase ; Choline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Among methylamine and/or ethylamine minus mutants of Arthrobacter P1 four different classes were identified, which were blocked either in the methylamine transport system, amine oxidase, hexulose phosphate synthase or acetaldehyde dehydrogenase. The results indicated that a common primary amine oxidase is involved in the metabolism of methylamine and ethylamine. Growth on ethylamine, however, was not dependent on the presence of the methylamine transport system. In mutants lacking amine oxidase, methylamine was unable to induce the synthesis of hexulose phosphate synthase, thus confirming the view that the actual inducer for the latter enzyme is not methylamine, but its oxidation product formaldehyde. Contrary to expectation, when the formaldehyde fixing enzyme hexulose phosphate synthase was deleted (mutant Art 11), accumulation of formaldehyde during growth on choline or on glucose plus methylamine as a nitrogen source did not occur. Evidence was obtained to indicate that under these conditions formaldehyde may be oxidized to carbon dioxide via formate, a sequence in which peroxidative reactions mediated by catalase are involved. In addition, a specific NAD-dependent formaldehyde dehydrogenase was detected in choline-grown cells of wild type Arthrobacter P1 and strain Art 11. This enzyme, however, does not play a role in methylamine or formaldehyde metabolism, apparently because these compounds do not induce its synthesis.
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  • 5
    ISSN: 1432-072X
    Keywords: Formate-hydrogen-lyase ; Upstream sequence ; Transcription start ; Deletion clones ; Hydrogenase 3 ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The regulatory elements involved in expression of the gene (fdhF) for the selenopolypeptide of formate dehydrogenase and of a gene (or transcriptional unit) (hyd) specifically responsible for the formation of the gas-evolving hydrogenase (hydrogenase 3) in Escherichia coli were investigated. Formate (or a product of it) is required for expression of both systems since in a pyruvate-formate-lyase deficient mutant induction occurs only when formate is supplemented externally. Under this condition, formate can partially overcome repression by nitrate. The transcription of both the fdhF gene and the hydrogenase-3-encoding systems is independent of the presence of a wild-type fnr gene when formate is present, supporting the view that the Fnr effect on the formation of the formate-hydrogen-lyase pathway is indirect. Mutations blocking the synthesis of a functional molybdenum cofactor also had no major affect on fdhF and hyd expression. The nucleotide sequence of the 5′ flanking region of the fdhF gene was determined and the transcription start point of the fdhF gene was localized by nuclease S1 mapping. Nuclease Bal31 generated deletion clones were constructed and the regulation of their expression was studied. Anaerobic expression and induction by formate depended on the presence of a stretch of approximately 185 nucleotides upstream of the translation start. Elements mediating formate induction and oxygen or nitrate repression could not be separated physically. The regulatory features of the fdhF upstream region bear striking resemblance to systems whose expression are dependent upon upstream activating elements.
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  • 6
    ISSN: 1432-072X
    Keywords: Nocardia sp. 239 ; Aromatic amino acids ; L-Phenylalanine ; DAHP synthase ; Chorismate mutase ; Prephenate dehydratase ; Anthranilate synthase ; Methylotrophy ; Regulation ; Methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The regulation of aromatic amino acid biosynthesis in Nocardia sp. 239 was studied. In cell-free extracts 3-deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) synthase activity was inhibited in a cumulative manner by tryptophan, phenylalanine and tyrosine. Chorismate mutase was inhibited by both phenylalanine and tyrosine, whereas prephenate dehydratase was very sensitive to inhibition by phenylalanine. Tyrosine was a strong activator of the latter enzyme, whereas anthranilate synthase was inhibited effectively by tryptophan. No clear repression of the synthesis of these enzymes was observed during growth of the organism in the presence of the aromatic amino acids. It is therefore concluded that in Nocardia sp. 239 synthesis of these amino acids is mainly regulated by feedback inhibition. The molecular organization and kinetic properties of DAHP synthase were studied in more detail following its purification. The molecular weight of the native enzyme and its single subunit species were estimated to be 168,000 and 41,000, respectively, suggesting that the enzyme is a tetramer. Apparent K m values for phosphoenolpyruvate (PEP) and erythrose-4-phosphate (E4P) were 45 and 370 μM, respectively. Tryptophan, phenylalanine and tyrosine inhibited DAHP synthase in a competitive manner with respect to E4P, with apparent K i values of 3, 160 and 180 μM, respectively. In addition, tryptophan and E4P (apparent K i values of 11 and 530 μM, respectively) were found to exert an uncompetitive and competitive inhibition, respectively, towards PEP.
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  • 7
    ISSN: 1432-072X
    Keywords: Phenoxyacetic acids ; Phenols ; Alcaligenes eutrophus JMP 134 ; Ortho-cleavage pathways ; Metacleavage pathway ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Alicaligenes eutrophus JMP 134 is able to grow on 2,4-dichloro-, 4-chloro-2-methyl- and 2-methylphenoxy acetic acid. The unsubstituted phenoxyacetic acid, however, is no growth substrate due to very poor induction of the 2,4-D monooxygenase. Spontaneous mutants of Alcaligenes eutrophus JMP 134 capable of growth with phenoxyacetic acid were selected on agar plates. One of these mutants, designated Alcaligenes eutrophus JMP 134-1, shows constitutive production of six enzymes of the 2,4-D pathway, which were known to be localized in at least three different transcriptional units. A common regulatory gene is postulated to be mutated. 2,4-Dichloro-, 4-chloro-2-methyl- and 2-methylphenoxyacetic acid were the inducers of the enzymes of the “chloroaromatic pathway” in Alcaligenes eutrophus JMP 134. Phenol and 2-methylphenol, metabolites of the degradation of phenoxyacetic acid and 2-methylphenoxyacetic acid, were shown to be inducers of the meta-cleavage pathway, whereas 2,4-dichlorophenol and 4-chloro-2-methylphenol were not. Thus efficient regulation prevents chloroaromatics from being misrouted into the unproductive meta-cleavage pathway. Because 2,4-dichloro-and 4-chloro-2-methylphenol did not show any induction potential, they were growth substrates only for the mutant strain JMP 134-1.
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  • 8
    ISSN: 1432-072X
    Keywords: Nocardia sp. 239 ; Phenylalanine dehydrogenase ; Phenylalanine ; Methanol ; Regulation ; Continuous culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In Nocardia sp. 239 d-phenylalanine is converted into l-phenylalanine by an inducible amino acid racemase. The further catabolism of this amino acid involves an NAD-dependent l-phenylalanine dehydrogenase. This enzyme was detected only in cells grown on l- or d-phenylalanine and in batch cultures highest activities were obtained at relatively low amino acid concentrations in the medium. The presence of additional carbon- or nitrogen sources invariably resulted in decreased enzyme levels. From experiments with phenylalanine-limited continuous cultures it appeared that the rate of synthesis of the enzyme increased with increasing growth rates. The regulation of phenylalanine dehydrogenase synthesis was studied in more detail during growth of the organism on mixtures of methanol and l-phenylalanine. Highest rates of l-phenylalanine dehydrogenase production were observed with increasing ratios of l-phenylalanine/methanol in the feed of chemostat cultures. Characteristic properties of the enzyme were investigated following its (partial) purification from l- and d-phenylalanine-grown cells. This resulted in the isolation of enzymes with identical properties. The native enzyme had a molecular weight of 42 000 and consisted of a single subunit; it showed activity with l-phenylalanine, phenylpyruvate, 4-hydroxyphenyl-pyruvate, indole-3-pyruvate and α-ketoisocaproate, but not with imidazolepyruvate, d-phenylalanine and other l-amino acids tested. Maximum activities with phenylpyruvate (310 μmol min-1 mg-1 of purified protein) were observed at pH 10 and 53°C. Sorbitol and glycerol stabilized the enzyme.
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  • 9
    ISSN: 1432-072X
    Keywords: Acetobacter methanolicus MB58 ; Methylotrophy ; Linear and cyclic dissimilatory sequence of formaldehyde ; Energy generation ; Mutants ; Regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Acetobacter methanolicus MB58 can grow on methanol. Since this substrate exhibits to be energy deficient there must be a chance to oxidize methanol to CO2 merely for purpose of energy generation. For the assimilation of methanol the FBP variant of the RuMP pathway is used. Hence methanol can be oxidized cyclically via 6-phosphogluconate. Since Acetobacter methanolicus MB58 possesses all enzymes for a linear oxidation via formate the question arises which of both sequences is responsible for generation of the energy required. In order to clarify this the linear sequence was blocked by inhibiting the formate dehydrogenase with hypophosphite and by mutagenesis inducing mutants defective in formaldehyde or formate dehydrogenase. It has been shown that the linear dissimilatory sequence is indispensable for methylotrophic growth. Although the cyclic oxidation of formaldehyde to CO2 has not been influenced by hypophosphite and with mutants both the wild type and the formaldehyde dehydrogenase defect mutants cannot grown on methanol. The cyclic oxidation of formaldehyde does not seem to be coupled to a sufficient energy generation, probably it operates only detoxifying and provides reducing equivalents for syntheses. The regulation between assimilation and dissimilation of formaldehyde in Acetobacter methanolicus MB58 is discussed.
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  • 10
    ISSN: 1432-072X
    Keywords: Rhodobacter sphaeroides ; Chlorobium limicola ; Thiocapsa roseopersicina ; Nitrogenase ; Regulation ; Ammonia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ammonia reversibly inhibits the nitrogenase activity not only in purple nonsulfur bacteria but in purple (Thiocapsa roseopersicina) and green (Chlorobium limicola forma thiosulfatophilum) sulfur bacteria as well. The complete inhibition of nitrogenase activity (acetylene reduction) is observed about 30 s after addition of NH 4 + (≥2.5×10-6 M) to cell suspensions. The pattern of ammonia inhibition of acetylene reduction in T. roseopersicina does not differ from the action of tetrabutylammonium and tetraphenylphosphonium (3 · 10-6-5·10-5 M) on nitrogenase activity of this bacterium. Simultaneously with the “switch-off” effect of NH 4 + a considerable increase of ATP in cells of Rhodobacter sphaeroides and C. limicola f. thiosulphatophilum was observed.
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