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  • 1
    ISSN: 1432-072X
    Keywords: Nitrogenase ; Methylamine ; Nitrogenase switch-off ; Rhodopseudomonas capsulata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the photosynthetic bacterium Rhodopseudomonas capsulata, NH 4 + switch-off of nitrogenase activity can be mimicked by its analog, methylamine. Like NH 4 + , methylamine appeared to require processing by glutamine synthetase (GS) before it was effective; γ-glutamylmethylamide was shown to be the product of this reaction. Evidence that this glutamine analog functioned directly to initiate nitrogenase inactivation was suggested first by the fact that it was a poor substrate for glutamate synthase (i.e., it was not further metabolized by this pathway) and secondly, azaserine which blocks the transfer of the glutamine amide group had no effect on CH3NH 3 + (or NH 4 + ) switch-off. These observations are taken as preliminary evidence to suggest that when NH 4 + inhibits nitrogenase activity, inactivation is initiated by glutamine itself, and not a molecule derived from it. Finally, evidence was presented that R. capsulata would use CH3NH 3 + as a nitrogen substrate, but lag periods and generation times increased with subsequent passages.
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  • 2
    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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  • 3
    ISSN: 1432-072X
    Keywords: Rhodospirillum rubrum ; Nitrogenase ; Glutamine synthetase NH inf4 sup+ switch off ; Complementation of R. rubrum Nif- mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A spontaneous pleiotropic Nif- mutation in Rhodospirillum rubrum has been partially characterized biochemically and by complementation analysis with recombinant plasmids carrying Azotobacter vinelandii DNA in the vicinity of ORF12 [Jacobson et al. (1989) J. Bacteriol 171:1017–1027]. In addition to being unable to grow on N2 as a nitrogen source the phenotypic characterization of this and other metronidazole enriched spontaneous mutants showed (a) no nitrogenase activity, (b) the absence of NifHDK polypeptides, (c) a slower growth rate on NH inf4 sup+ , (d) approximately 50% higher glutamine synthetase (GS) activity than the wild-type, which was repressible, (e) an inability to switch-off GS activity in response to an NH inf4 sup+ up-shift, and (f) an inability to modify (32P-label) the GS polypeptide. The apparent relationship between the absence of nifHDK expression and the absence of GS adenylylation cannot be explained in terms of the current model for nif gene regulation. However, R. rubrum transconjugants receiving A. vinelandii DNA which originated immediately upstream from nifH, restored all aspects of the wild-type phenotype. These data suggest a here-to-fore unrecognized relationship between nif expression and GS switch-off (adenylylation) activity, and the existence of a previously unidentified regulatory locus in Azotobacter that complements this mutation.
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  • 4
    ISSN: 1432-072X
    Keywords: Nitrogenase ; NH 4 + switch-off ; Rhodobacter sphaeroides ; Methylosinus trichosporium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In vivo switch-off of nitrogenase activity by NH 4 + is a reversible process in Rhodobacter sphaeroides and Methylosinus trichosporium OB3b. The same pattern of switch-off in Rhodospirillum rubrum is explained by ADP-ribosylation of one of the Fe protein subunits, however, no evidence of covalent modification could be found in the subunits from either R. sphaeroides or M. trichosporium. Fe protein subunits from these organisms showed no variant behaviour on SDS-PAGE, nor were they 32P-labeled following switch-off. These observations suggest either that the attachment of the modifying group to the Fe protein in these organisms is quite labile and does not survive in vitro manipulation, or that the mechanism of switch-off is different than that seen in Rhodospirillum.
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  • 5
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
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  • 6
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The volatile forms of selenium emitted from soils and plants have been identified by others as dimethylselenide and dimethyldiselenide. Dimethylselenoniopropionate, a possible precursor of dimethylselenide, is the selenium analogue of the common marine osmoprotectant, dimethylsulfoniopropionate. Dimethylselenoniopropionate was organically synthesized from dimethylselenide and acrylate and used in a comparative study with dimethylsulfoniopropionate as a growth substrate, an inducer and substrate for dimethylsulfoniopropionate lyase in two marine bacterial isolates, Alcaligenes sp. strain M3A and Pseudomonas doudoroffii, and in salt marsh sediments and estuarine creek water samples. In P. doudoroffii, the rate of dimethylselenoniopropionate transport into cells was about half that observed with dimethylsulfoniopropionate; Alcaligenes does not take up these molecules. The rate and extent of induction of dimethylsulfoniopropionate lyase in P. doudoroffii at low concentrations of dimethylselenoniopropionate were similar to that of dimethylsulfoniopropionate. In Alcaligenes the low constitutive level of dimethylsulfoniopropionate lyase cleaved dimethylselenoniopropionate into dimethylselenide and acrylate, but induction of dimethylsulfoniopropionate lyase by dimethylselenoniopropionate did not follow. Dimethylsulfoniopropionate lyases from both strains, when induced by dimethylsulfoniopropionate, utilized dimethylselenoniopropionate as a substrate with emission of dimethylselenide. Rates of partially purified dimethylsulfoniopropionate lyase activity with dimethylselenoniopropionate were half those with dimethylsulfoniopropionate. Anoxic salt marsh sediments catalyzed dimethylsulfoniopropionate and dimethylselenoniopropionate degradation at equal rates. In sediments containing high organic matter, both dimethylsulfide and dimethylselenide served as substrates for methanogenesis. These data support the hypothesis that organic selenium molecules can be volatilized by the same biochemical pathways as organic sulfur molecules.
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  • 7
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The regulatory properties of Rhodospirillum rubrum nitrogenase reduced by either the endogenous electron donor (ferredoxin) or an artificial donor (dithionite) were examined. The nitrogenase obtained from glutamate-grown cells required activating enzyme for maximum activity with either reductant. The activating enzyme requirement of ferredoxin-dependent nitrogenase activity implies a physiological significance of the activating enzyme in R. rubrum. Rhodopseudomonas capsulata nitrogenase also required activating enzyme when dithionite was the reductant, but there appeared to be no activating enzyme requirement with ferredoxin as the reductant. Because the catalytic activity of the enzyme was very low under these conditions, the physiological significance of activating enzyme in this organism remains in question.
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  • 8
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Freshwater river sediments from both the Coastal Plain and Piedmont regions of South Carolina showed high rates of dimethylsulfide (DMS) production from added dimethylsulfoniopropionate (DMSP). These rates were considered to be high as they were ca. 1% of rates in salt marsh sediments. Most probable number enumeration of DMS producers in river water and sediments were also about 1% of those measured in estuarine water and salt marsh sediment. Tellurite and DMSP enrichments resulted in the isolation of tellurite-resistant Gram-positive nocardia-like DMS producers from freshwater, but not marine sediments. Gram-negative DMS producers, all capable of growth on DMSP, were isolated from both freshwater and salt marsh sediments. Sequencing the 16S rRNA genes of the most common freshwater isolates showed they were closely related to Rhodococcus equi and Rhodococcus rhodochrous, members of the family Nocardiaceae. This group, which made up 73% of the total number of freshwater sediment isolates, belonged to the phylogenetic class of high-GC, Gram-positive bacteria, a newly recognized group of DMS producers. The origin of DMSP-dependent DMS producers in a freshwater, nearly DMSP-free, environment is discussed.
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  • 9
    ISSN: 1573-5079
    Keywords: 7Fe Ferredoxin ; Rhodospirillum rubrum ; Fe-S clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The complete sequence of amino acids of ferredoxin II (FdII) from Rhodospirillum rubrum was determined by repetitive Edman degradation using pyridylethylated-ferredoxin and oxidized, denatured ferredoxin. Peptides derived from trypsin, pepsin, Glu-C endoproteinase, Arg-C endoproteinase, tryptophan specific cleavage and partial acid hydrolysis and C-terminal sequence from carboxypeptidase digestion were used to construct the total sequence. RrFdII is a polypeptide of 104 amino acids having a calculated molecular weight of 11556 excluding the iron and sulfur atoms. The complete amino acid sequence was: PYVVTENCIKCKYQDCVEVCPVDCFYEGENFLVINPDECIDCGVCNPECPAEAIAGKWLEINRKFADLWPNITRKGPAL ADADDWKDKPDKTGLLSENPGKGTV. Sequence comparisons, EPR characteristics and iron analyses indicate that RrFdII has structural features in common with ferredoxins containing [3Fe-4S], [4Fe-4S] centers. Of 104 amino acids, 60 (58%) including all 9 cysteines, are found in identical locations in the 7Fe ferredoxin prototype, Azotobacter vinelandii FdI.
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