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  • 1
    Electronic Resource
    Electronic Resource
    Isolation and characterization of xanthine dehydrogenase from Chlamydomonas reinhardtii (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 72 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Xanthine dehydrogenase (XDH, EC 1.2.1.37) of Chlamydomonas reinhardtii (Sager) 6145c wild strain has been isolated and characterized for the first time in a unicellular green alga. The enzyme has an Mr of 330 kDa, and FAD, molybdenum and iron are cofactors required for its activity as deduced from results obtained using specific inhibitors, 59Fe-labelling experiments, activity protection by FAD, physiological responses in vivo to iron and molybdenum deficiencies in the culture medium and work with mutants lacking molybdenum cofactor. Xanthine dehydrogenase exhibited Mi-chaelian kinetics typical for a bisubstrate enzyme with apparent Km values for NAD +, hypoxanthine and xanthine of 35, 160 and 70 μM, respectively. Under phototrophic conditions enzyme activity was repressed by ammonium, but xanthine was not required for the enzyme to be induced, since high levels of enzyme activity were found in cells grown on ammonium and transferred to either N-frec media or media containing either of the nitrogen sources adenine, urea, urate, xanthine, hypoxanthine and guanine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb06629.x
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  • 2
    Electronic Resource
    Electronic Resource
    Inorganic carbon transport across cell compartments of the halotolerant alga Dunaliella salina (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 85 (1992), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The inorganic carbon (Ci) accumulation and the intracellular location of carbonic anhydrase (CA, EC 4.2.1.1) in the halotolerant unicellular alga Dunaliella salina have been investigated. The rate of HCO3 -dependent O2 evolution was determined by growth conditions. Algae grown under high CO2 conditions (5% CO2 in air, v/v; high Ci cells) had a very low affinity for HCO3− at pH 7.0 and 8.2, whereas algae grown under low CO2 conditions (0.03% CO2 in air; low Ci cells) showed a high affinity for HCO3− at both pH values and were sensitive to Dextran-bound sulfonamide (DBS), an inhibitor of extracellular CA. The photosynthetic rate or HCO4− dependent O2 evolution was always higher at pH 7.0 than at pH 8.2. Ethoxyzolamide (EZ), an inhibitor of total (extacellular plus intracellular) CA activity, strongly inhibited photosynthesis at both pH values. During adaptation from high to low CO2 conditions CA activity increased in chloroplasts in a process dependent on the novo protein synthesis. Carbonic anhydrase activity was found in the supernatant and pellet fractions of chloroplast homogenates. The rate of photosynthesis of chloroplasts from low Ci cells was higher at pH 7.0 than at pH 8.2. The alkalinization of the growth medium, which took place only in the presence of Ci, was partially inhibited by DBS and completely by EZ. We suggest that in D. salina CO2 is the general form of Ci transported across the plasma membrane and the chloroplast envelope and that bicarbonate enters the cell mainly, although not entirely, by an ‘indirect’ mechanism after dehydration to CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1992.tb04713.x
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  • 3
    Electronic Resource
    Electronic Resource
    Urate oxidase of Chlamydomonas reinhardii (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 62 (1984), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Urate oxidase (EC 1.7.3.3) of Chlamydomonas reinhardii cells grown on purines and purine derivatives has been partially characterized. Crude enzyme preparations have a pH optimum of 9.0, require O2 for activity, have an apparent Km of 12 μM for urate, and are inhibited by high concentrations of this substrate. Enzyme activity was particularly sensitive to metal ion chelating agents like cyanide, cupferron, diethyldithiocarbamate and o-phenanthroline, and to structural analogues of urate like hypoxanthine and xanthine. Chlamydomonas cells grow phototrophically on adenine, guanine, hypoxanthine, xanthine, urate, allantoin or allantoate as sole nitrogen source, indicating that in this alga the standard pathway of aerobic degradation of purines of higher plants, animals and many microorganisms operates. As deduced from experiments in vivo, urate oxidase from Chlamydomonas is repressed in the presence of ammonia or nitrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb04602.x
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  • 4
    Electronic Resource
    Electronic Resource
    Photorespiratory ammonium assimilation in chloroplasts of Chlamydomonas reinhardtii (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 91 (1994), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of CO2 concentration on the rate of photorespiratory ammonium excretion and on glutamine synthetase (GS) and carbonic anhydrase (CA) isoenzymes activities has been studied in Chlamydomonas reinhardtii cw-15 mutant (lacking cell wall) and in the high CO2-requiring double mutant cia-3/cw-15 (lacking cell wall and chloroplastic carbonic anhydrase). In cw-15 cells, both the extracellular (CAext) and chloroplastic (CAchl) CA activities increased after transferring cells from media bubbled with 5% CO2 in air (v/v, high-Ci cells) to 0.03% CO2 (low-Ci cells), whereas in cia-3/cw-15 cells only the CAext was induced after adaptation to low-Ci conditions and the CAchl activity was negligible. During adaptation to low-Ci conditions in the presence of 1 mM of l-methionine-D,L-sulfoximine (MSX), a specific inhibitor of GS activity, both mutant strains excreted photorespiratory ammonium into nitrogen free medium. In addition, the ammonium excretion rate by cw-15 in the presence of MSX was lower in cells grown and kept at 5% CO2 than in high-Ci cells adapted to 0.03% CO2. The double mutant cia-3/cw-15 excreted photorespiratory ammonium at a higher rate than did cw-15. Total GS activity (GS-1 plus GS-2) increased during adaptation to 0.03% CO2 in both strains of C. reinhardtii. However, only the activity GS-2, which is located in the chloroplast, increased during the adaptation to low CO2, whereas the cytosolic GS-1 levels remained similar in high and low-Ci cells. We conclude that: (1) cia-3/cw-15 cells lack chloroplastic CA activity; (2) in C. reinhardtii photorespiratory ammonium is refixed in the chloroplasts through the GS-2/GOGAT cycle; and (3) chloroplastic GS-2 concentration changes in response to the variation of environmental CO2 concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb02979.x
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  • 5
    Electronic Resource
    Electronic Resource
    Occurrence of an NADH diaphorase activity associated with xanthine dehydrogenase in Chlamydomonas reinhardtii (1987)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 43 (1987), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Wild-type Chlamydomonas reinhardtii cells exhibited a peculiar NADH-nitrobluetetrazolium reductase (NADH diaphorase) activity when grown under conditions in which xanthine dehydrogenase (XDH) is present. This XDH-coinduced diaphorase was electrophoretically distinguishable from constitutive diaphorases, showed the same mobility as XDH and could be assayed in vitro with dichlorophenol indophenol. Mutant strains 102, 104 and 307 of Chlamydomonas which lack XDH did not exhibit XDH-coinduced diaphorase. Heat treatment of crude extracts or partial purification of XDH inactivated or removed all constitutive diaphorases and left significant levels of XDH-coinduced diaphorase which remained always associated with XDH. These results demonstrate that XDH from C. reinhardtii, like other organisms, is also capable of catalyzing NADH oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1987.tb02166.x
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  • 6
    Electronic Resource
    Electronic Resource
    In vivo short-term inhibition of nitrogenase by nitrate in Rhodopseudomonas capsulata E1F1 (1986)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 34 (1986), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Rhodopseudomonas capsulata E1F1, a purple non-sulfur bacterium capable of photoassimilating nitrate, could fix N2 in the presence of nitrate until nitrite traces originated by nitrate reduction were excreted to the medium. Nitrite excretion resulted in the immediate cessation of dinitrogen fixation that was resumed once nitrite was assimilated. Although nitrite addition strongly inhibited N2 fixation, nitrate did not affect nitrogenase in whole cells unless it was first reduced to nitrite. After 2.5 h of nitrite treatment, nitrogenase activity recovered upon nitrite elimination in a process independent from de novo protein synthesis. A similar nitrate inhibition of nitrogenase was found in a Rhodopseudomonas sphaeroides strain able to reduce nitrate. In contrast, nitrogenase of other strains incapable of reducing nitrate was unaffected by nitrate, but immediately inhibited by nitrite. The effect of nitrate on nitrogenase in Rp. capsulata E1F1 is then interpreted in terms of a short-term inhibition by nitrite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1986.tb01358.x
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  • 7
    Electronic Resource
    Electronic Resource
    Involvement of sulphydryl groups in glutamine synthetase activity from Rhodobacter capsulatus E1F1 (1987)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 41 (1987), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Glutamine synthetase (GS) from the phototrophic bacterium Rhodobacter capsulatus E1F1 (formerly known as Rhodopseudomonas capsulata E1F1) contains 9 SH-groups per subunit. These SH-groups reacted with sulphydryl group reagents resulting in an inhibition of the transferase activity of GS. Inhibited GS was recovered up to 90% of its initial value by treatment with thiols such as l-cysteine, dithiothreitol, or 2-mercaptoethanol. However, dithioerythritol exhibited, at concentrations above 0.5 mM, a significant inhibition of the transferase activity. Glutamine and glutamate protected against the inactivation by sulphydryl group reagents, whereas ADP or ATP enhanced the velocity of inactivation considerably. Mn2+-dependent GS was unaffected in vivo by light-dark transitions, which rules out a redox photoregulation of SH-groups required for activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1987.tb02132.x
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  • 8
    Electronic Resource
    Electronic Resource
    Glutamate dehydrogenase isozymes of Chlamydomonas reinhardtii (1989)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 61 (1989), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract In Chlamydomonas reinhardtii there are three glutamate dehydrogenase isozymes which can use both NADH and NADPH as cofactors and respond differently to different nitrogen sources and several stress conditions. From data of induction of isozymes in different metabolic situations, we propose a possible physiological role for each of them in algal carbon and nitrogen metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1989.tb03643.x
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  • 9
    Electronic Resource
    Electronic Resource
    Acetate metabolism in purple non-sulfur bacteria (1989)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 58 (1989), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The photosynthetic non-sulfur purple bacterium Rhodobacter capsulatus E1F1 can grow on acetate or dl-malate photoheterotrophically under anerobic conditions or chemoheterotrophically in the dark in the presence of dioxygen. Bacterial cells grown under both anaerobic and aerobic conditions exhibited high amounts of the tricarboxylic acid cycle enzymes especially in dark-aerobic cultures. A high activity of isocitrate lyase was found in cells of R. capsulatus E1F1 and, to a lesser extent, in those of R. capsulatus IP2, Rhodobacter sphaeroides and Rhodospirillum rubrum grown photoheterotrophically on acetate under anaerobic conditions. The second enzyme of the glyoxylate shunt, malate synthase, appears to be constitutive. Itaconate, a powerful inhibitor of isocitrate lyase, severely inhibited growth of R. capsulatus, R. rubrum and R. sphaeroides on acetate, thus corroborating a physiological role of the enzyme in acetate metabolism by Rhodospirillaceae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-6968.1989.tb03032.x
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  • 10
    Electronic Resource
    Electronic Resource
    Regulation of reduced nitrogen assimilation in Rhodobacter capsulatus E1F1 (1989)
    Springer
    Archives of microbiology 152 (1989), S. 508-511 
    Details
    ISSN: 1432-072X
    Keywords: Rhodobacter capsulatus ; Glutamine synthetase ; Glutamate synthase ; l-alanine dehydrogenasc ; Aminotransferase activities ; l-asparaginase ; Metabolic regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phototrophic bacterium Rhodobacter capsulatus E1F1 assimilates ammonia and other forms of reduced nitrogen either through the GS/GOGAT pathway or by the concerted action of l-alanine dehydrogenase and aminotransferases. These routes are light-independent and very responsive to the carbon and nitrogen sources used for cell growth. GS was most active in cells grown on nitrate or l-glutamate as nitrogen sources, whereas it was heavily adenylylated and siginificantly repressed by ammonium, glycine, l-alanine, l-aspartate, l-asparagine and l-glutamine, under which conditions specific aminotransferases were induced. GOGAT activity was kept at constitutive levels in cells grown on l-amino acids as nitrogen sources except on l-glutamine where it was significantly induced during the early phase of growth. In vitro, GOGAT activity was strongly inhibited by l-tyrosine and NADPH. In cells using l-asparagine or l-aspartate as nitrogen source, a concerted induction of l-aspartate aminotransferase and l-asparaginase was observed. Enzyme level enhancements in response to nitrogen source variation involved de novo protein synthesis and strongly correlated with the cell growth phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00446938
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