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1981 (1)
1980 (1)
1Author    Werner Aretz, Herwig Kaspari, Jobst-Heinrich KlemmeRequires cookie*
 Title    Molekulare und kinetische Charakterisierung der Xanthin-Dehydrogenase aus dem phototrophen Bakterium Rhodopseudomonas capsulata Molecular and Kinetic Characterization of Xanthine Dehydrogenase from the Phototrophic Bacterium Rhodopseudomonas capsulata  
 Abstract    The structural and kinetic properties of xanthine dehydrogenase (EC 1.2.1.37) from the facultative phototrophic bacterium Rhodopseudomonas capsulata were studied. The enzyme was fully induced when hypoxanthine or xanthine, but less effectively when uric acid served as nitrogen source during growth. The enzyme was purified about 2300-fold from cells grown photosynthetically with hypoxanthine as N-source by using ammoniumsulfate precipitation, gel filtration, ion-exchange and affinity chromatography. The molecular weight as determined by gel filtration throug Sephacryl S-300 was 345000. Subunit analysis by sodium dodecyl sulfate gel electrophoresis suggested a composition o f four identical subunits with a molecular weight o f 84000. The enzyme contained 2 flavin, 2 molybdenum and 8 iron-sulfur groups per mol. The turnover number with hypoxanthine and NAD as substrates was 12000 min-1. Hypoxanthine, 1-methylhypoxanthine, 8-azahypoxanthine, xanthine, 1-methylxanthine, 2-hydroxypurine, 6,8-di-hydroxypurine, 5-azacytosine and 5-azauracil served as electron donors. The most effective electron acceptor was NAD. The kinetic constants (K m) were (in (i m): 52.5 (hypoxanthine); 32.5 (xanthine) and 61.2 (NAD). Various purine compounds inhibited the enzyme competitively in respect to hypoxanthine as substrate. Although reduction of uric acid to xanthine was not detected by using purified enzyme preparations, in v;>o-experiments with 14C-labelled uric acid indicated that the enzyme xanthine dehydrogenase participates in uric acid degradation in Rps. capsulata. According to their electrophoretic mobilities, the xanthine dehydrogenases isolated from hypoxanthine-and uric acid-grown cells were identical. 
  Reference    Z. Naturforsch. 36c, 933—941 (1981); received July 10 1981 
  Published    1981 
  Keywords    Xanthine Dehydrogenase, Phototrophic Bacteria, Rhodopseudomonas capsulata 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0933.pdf 
 Identifier    ZNC-1981-36c-0933 
 Volume    36 
2Author    Eckhard BastRequires cookie*
 Title    Ammonia Assimilation by Thiocapsa roseopersicina Grown on Various Nitrogen and Carbon/Electron Sources  
 Abstract    Batch cultures o f the phototrophic bacterium, Thiocapsa roseopersicina, were grown anaero­ bically in the light either on sulfide with various ammonia concentrations, N 2 or amino acids as nitrogen sources, or on several simple organic substrates in the absence o f reduced sulfur com­ pounds using 6 mM N H 4C1 as source o f nitrogen. At high ammonia concentrations high activities of (NADPH-linked) glutamate dehydrogenase (GDH), but rather low transferase and no bio­ synthetic activity of glutamine synthetase (GS) were obtained, while under conditions o f ammonia deficiency (growth with N 2 or glutamate) GDH activity was very low and both GS activities were strongly increased. Glutamate synthase (GOGAT) activity (NADH-dependent) showed little variation. These data indicate that at high NH+ concentrations ammonia is assimilated via GDH, under NHJ limitation, however, via the G S/G O G A T system. Glutamine as nitrogen source may be utilized via GOGAT as well as via an active glutaminase plus GDH. Ammonia, but not glutamine, seems to cause repression and inactivation of GS. Alanine and asparagine inactivate the enzyme inhibiting the biosynthetic, but not the transferase activity. These amino acids in part also influence the activities o f GDH, GOGAT, malate dehydrogenase (MDH) and isocitrate dehydro­ genase (ICDH). Cultures grown on acetate or pyruvate instead of sulfide showed increased GDH activities and high GS transferase activities possibly reflecting an increase o f intracellular a-ketoglutarate con­ centration. On malate or fructose also increased GS transferase activities, but rather low GDH activities were observed. High biosynthetic GS activities and elevated GOGAT activities were found only in fructose-grown cells. On the organic substrates the ICDH activities always were somewhat higher than after lithoautotrophic growth. With the exception of acetate, the MDH activities were considerably elevated, especially on pyruvate. The different pathways of ar-keto-glutarate formation and their influence on the enzymes of ammonia assimilation are discussed. 
  Reference    Z. Naturforsch. 35c, 439 (1980); received December 17 1979 
  Published    1980 
  Keywords    Thiocapsa roseopersicina, Phototrophic Bacteria, Nitrogen Sources, Ammonia Assimilation, Carbon Metabolism 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0439.pdf 
 Identifier    ZNC-1980-35c-0439 
 Volume    35