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  • 1
    ISSN: 1432-072X
    Keywords: d-Ribulose 1,5-diphosphate carboxylase ; Oxygenase activity ; Quaternary structure ; Electron microscopy ; Alcaligenes eutrophus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract d-Ribulose 1,5-diphosphate carboxylase has been purified from autotrophically grown cells of the facultative chemolithotrophic hydrogen bacteriumAlcaligenes eutrophus. The enzyme was homogeneous by the criteria of polyacrylamide gel electrophoresis. The molecular weight of the enzyme was 505000 determined by gel filtration and sucrose density gradient centrifugation, and a sedimentation coefficient of 18.2 S was obtained. It was demonstrated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis that the enzyme consists of two types of subunits of molecular weight 52000 and 13000. Electron microscopy on the intact and the partially dissociated enzyme lead to the construction of a model for the quaternary structure of the enzyme which is composed of 8 large and 8 small subunits. The most probable symmetry of the enzyme molecule is 4:2:2. Michaelis constant (K m ) values for ribulose 1,5-diphosphate, Mg2-, and CO2 were 0.59 mM, 0.33 mM, and 0.066 mM measured under air. Oxygen was a competitive inhibitor with respect to CO2 suggesting that the enzyme also exhibits an oxygenase activity. The oxygenolytic cleavage of ribulose 1,5-diphosphate was shown and a 1:1 stoichiometry between oxygen consumption and 3-phosphoglycerate formation observed.
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  • 2
    ISSN: 1432-072X
    Keywords: Glycollate excretion ; Phosphoglycol-late phosphatase ; Glycollate oxidoreductase ; d-Ribulose 1,5-diphosphate carboxylase ; Alcaligenes eutrophus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Autotrophic cultures of the facultative chemolithotrophAlcaligenes eutrophus have been found to excrete glycollate. This excretion was greatly stimulated by the incorporation of up to 20% (v/v) oxygen in the hydrogen used for gassing. The stimulatory effect of oxygen was prevented by the addition of 10% (v/v) CO2 to the gassing mixture. Glycollate excretion only in the presence of oxygen was increased by the addition of 2-pyridyl-hydroxymethane sulphonic acid (HPMS), an inhibitor of glycollate oxidation, indicating that glycollate formation itself was stimulated by oxygen. No glycollate excretion by cultures grown heterotrophically on pyruvate was detected, either in the absence or presence of HPMS, under heterotrophic or autotrophic conditions. Extracts from autotrophic cells showed phosphoglycollate phosphatase and glycollate oxidoreductase activities, which were considerably lower in extracts prepared from pyruvate- or fructose-grown (heterotrophic) cells. The increase in activity of both enzymes upon cell transfer from heterotrophic to autotrophic growth was prevented by chloramphenicol and resembled the induction ofd0ribulose 1,5-diphosphate carboxylase under the same conditions.
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  • 3
    ISSN: 1432-072X
    Keywords: R-Bodies ; Kappa particles ; Free-living hydrogen bacteria ; Induction ; Electron microscopy ; Chemical composition ; Defective prophages ; Plasmids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract R-Bodies have been found in a recently isolated pseudomonas-like free-living hydrogen oxidizing bacterium. Their isolation, fine structure and chemical composition are described and compared with the R-bodies from the kappa particles (Caedobacter), obligate endosymbionts of Paramecium aurelia. The 2K 1 R-bodies exhibited essential characteristics of the kappa R-bodies; however, their size and some other structural aspects proved that they represent a new type of R-bodies. The presence of phage tail-like particles in cells induced with Mitomycin C is in favour of the hypothesis that the R-bodies might be coded by defective prophages, or by extrachromosomal elements.
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  • 4
    ISSN: 1432-072X
    Keywords: Aquaspirillum autotrophicum ; Hydrogen bacterium ; Growth ; Chemolithoautotrophy ; Particulate hydrogenase ; Induction ; Repression ; Natural habitats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aquaspirillum autrotrophicum, an aerobic hydrogen bacterium recently isolated from an eutrophic freshwater lake, was characterized physiologically. It grew autotrophically in a fermenter with a doubling time of 4 h. Heterotrophic growth was faster. pH-Optimum ranged from 5.0–7.5, temperature optimum was about 28° C. During autotrophic growth about 10 moles hydrogen were consumed per 1 mole carbon dioxide fixed. Hydrogenase activity is inducible. CO2 did not enhance the oxy-hydrogen reaction by intact cells. The hydrogenase activity was localized in the particulate fraction. The hydrogenase reduced methylene blue and phenazine methosulfate; pyridine nucleotides were not reduced. In cell-free extracts, hydrogenase was sensitive to oxygen. Ribulosebisphosphate carboxylase was present in autotrophically-grown cells and absent from heterotrophically grown cells. Hydrogenase induction in heterotrophically-grown cells followed parabolic kinetics. Oxygen and D-gluconate repressed hydrogenase synthesis, whereas citrate, DL-lactate and pyruvate stimulated its formation. The repressive effect was delayed. The results suggest that the control of hydrogenase synthesis occurred at the transcriptional level, and that mRNA coding for the hydrogenase had a relatively long life span. D-Gluconate was degraded via the Entner-Doudoroff pathway, the enzymes of which were constitutively formed. Enzymes of the pentosephosphate and Embden-Meyerhof pathways (except phosphofructokinase) were present, too. Hydrogen did not inhibit heterotrophic growth. The possible competitive advantage of the physiological properties described with regard to the natural habitat was discussed.
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