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1Author    Thom As Urbig, Rüdiger Schulz, H. Orst SengerRequires cookie*
 Title    Inactivation and Reactivation of the Hydrogenases of the Green Algae Scenedesmus obliquus and Chlamydomonas reinhardtii  
 Abstract    The hydrogenases of the green algae Scenedesmus obliquus and Chlamydomonas reinhardtii were activated under anaerobic conditions. Exposure o f whole cells and cell-free homogenates to air lead to a complete inactivation of the hydrogenases. The inactivation in whole cells of Scenedesmus is faster than the inactivation of the cell-free homogenate. Inactivation o f the hy­ drogenases could be reversed by anaerobic readaptation in whole cells. The inactivation of the hydrogenase in homogenates seems to be irreversible. N either the removal o f oxygen nor the addition of ATP, N AD(P)H, sodium dithionite, dithiothreitol, ferredoxin and thioredoxin to homogenates facilitated the reactivation o f the hydrogenase. The occurrence of a hydrogenase regulating factor is discussed. 
  Reference    Z. Naturforsch. 48c, 41 (1993); received September 30/December 21 1992 
  Published    1993 
  Keywords    Scenedesmus obliquus, Chlamydomonas reinhardtii, Hydrogenase, Reactivation Process, Inactivation 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0041.pdf 
 Identifier    ZNC-1993-48c-0041 
 Volume    48 
2Author    Kiriakos Kotzabasis3, D. Ieter, D. Örnem AnnbRequires cookie*
 Title    Differential Changes in the Photosynthetic Pigments and Polyamine Content during Photoadaptation and Photoinhibition in the Unicellular Green Alga Scenedesmus obliquus  
 Abstract    In the unicellular green alga Scenedesmus obliquus the level o f photoinhibition and the recovery of the cells after reversal to the initial light conditions in relation to the pre-photo-adaptation of the culture to low, medium and high light intensity was determined. The changes in the photosynthetic pigment content and in the intracellular polyam ine concentra­ tion allowed to distinguish between photoadaptation and photoinhibition. In particular, the level of chlorophylls, xanthophylls and carotenoids decreased inversely proportional to the light intensity applied during photoadaptation, whereas their concentrations remained con­ stant during photoinhibition. The violaxanthin/zeaxanthin and the loroxanthin/lutein cycle work only under photoinhibitory conditions, but not under photoadaptive premises. Changes in the level of these carotenoids in relation to the changes in the photosynthetic apparatus during photoadaptation are discussed. In addition, it was found that the intracellular polya­ mine level increased only under stress conditions, i. e. during photoinhibition, and decreased during recovery of the cells after reversal to the initial light conditions. The increase of the putrescine level during photoinhibition is inversely proportional to the light intensity used for pre-adaptation. This rise of the polyamine level in the cells photoadapted to high light conditions is an additional indication for the finding that photoadaptation and photoinhibi­ tion are different phenomena which are clearly distinguishable from each other. Finally, the changes of the chlorophyll, violaxanthin, zeaxanthin, loroxanthin, lutein and polyamine levels under photoadaptation in high light intensity (50 W m '2) in relation to the range of photo­ adaptation in Scenedesmus obliquus are discussed. 
  Reference    Z. Naturforsch. 53c, 833—8 (1998); received May 8/June 15 1998 
  Published    1998 
  Keywords    Polyamines, Photosynthetic Apparatus, Photoinhibition, Photoadaptation, Scenedesmus obliquus 
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 TEI-XML for    default:Reihe_C/53/ZNC-1998-53c-0833.pdf 
 Identifier    ZNC-1998-53c-0833 
 Volume    53 
3Author    Rüdiger Hofm, H. Artm, Ut FollmannRequires cookie*
 Title    Bleom ycin-Iron C om plex and Oxygen Activate Algal R ibonucleotide Reductase  
 Abstract    Ribonucleotide reductase of green algae (Scenedesmus obliquus) is a radical-containing enzyme which rapidly loses activity under anaerobic conditions. Reactivation in the presence of air is enhanced by 10 |j.m iron(II)-bleomycin chelate. The reaction lends new biochemical potential to the antibiotic and should be valuable in mechanistic studies of ribonucleotide reduction. 
  Reference    Z. Naturforsch. 40c, 919—921 (1985); received August 22 1985 
  Published    1985 
  Keywords    Bleomycin, Deoxyribonucleotide Synthesis, Iron, Oxygen Dependence, Ribonucleotide Reduction, Scenedesmus obliquus 
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 TEI-XML for    default:Reihe_C/40/ZNC-1985-40c-0919_n.pdf 
 Identifier    ZNC-1985-40c-0919_n 
 Volume    40 
4Author    Beate Klein, Hartmut FollmannRequires cookie*
 Title    Deoxyribonucleotide Biosynthesis in Green Algae. S Phase-Specific Thymidylate Kinase and Unspecific Nucleoside Diphosphate Kinase in Scenedesmus obliquus  
 Abstract    NDP kinase and thymidylate kinase are essential for DNA precursor formation in that they phosphorylate the products of de novo deoxyribonucleotide biosynthesis, deoxyribonucleoside 5'-diphosphates and thymidine 5'-monophosphate to the corresponding triphosphates which then serve as DNA polymerase substrates. The two enzymes have been measured in synchronous cultures of the green algae, S. obliquus. Thymidylate kinase exhibits an activity peak at the 11 —12th hour of the 24-hour cell cycle, coinciding with DNA synthesis. Enzyme activity is markedly stimulated in presence of fluorodeoxyuridine in the culture medium. This behaviour of dTMP kinase is very similar to that of three other S phase-specific peak enzymes previously analyzed in synchronous algae, viz. ribonucleotide reductase, thymidylate synthase, and dihydro-folate reductase. In contrast, NDP kinase exhibits high and constant activity through the entire cell cycle. The two kinases have been isolated from cell-free extracts, and separated from each other by chromatography on Blue Sepharose. The peak enzyme, dTMP kinase, has been purified to near homogeneity and its catalytic properties are described; the molecular weight is 56,000. NDP kinase activity is separable into two enzyme fractions, both of molecular weight 100,000 (or higher), which are unspecific with respect to ribonucleotide and deoxyribonucleotide substrates. Characterization and purification of the whole series of deoxyribonucleotide-synthesizing enzymes from one organism provides a basis for in vitro experiments towards reconstitution of an S phase-specific DNA precursor/DNA replication multien-».yme aggregate. 
  Reference    Z. Naturforsch. 43c, 377—385 (1988); received February 12/March 17 1988 
  Published    1988 
  Keywords    Algae, Cell Cycle, Deoxyribonucleotides, Nucleoside Diphosphate Kinase, Scenedesmus obliquus 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0377.pdf 
 Identifier    ZNC-1988-43c-0377 
 Volume    43