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'D 1 Turnover' in keywords
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1990 (2)
1Author    Nir Ohad3, Dekel Amir-Shapirab, Hiroyuki Koikec, Yorinao Inouec, Itzhak Ohadb, Joseph Hirschberg3Requires cookie*
 Title    Amino Acid Substitutions in the D 1 Protein of Photosystem II Affect Q b-Stabilization and Accelerate Turnover of D  
 Abstract    Isogenic strains of Synechococcus PCC 7942 were genetically engineered so that copy I of the gene psbA was mutated at specific sites. These mutations resulted in replacements of Ser 264 by Gly or Ala and of Phe 255 by Tyr or Leu in the D 1 protein. The mutants were resistant to herbicides inhibiting electron transfer in photosystem II. All mutants exhibited alterations in the stability of Q B' as demonstrated by a temperature downshift, to various extents, of the in vivo thermoluminescence emission. Measurements of the light-dependent turnover of D 1 showed a marked decrease in the 11 / 2 of this protein in the mutants as compared to wild-type, under low to medium light intensities. A correlation was found between the degree of pertur­ bation in the Q B" stability and the rate of acceleration in the turnover of D 1. These data pro­ vide a direct evidence for the overlapping binding sites for the plastoquinone B and herbicides in the D 1 protein. In addition these data indicate a close link between Q B" destabilization in reaction center II and the mechanism controlling the light-dependent turnover of D 1. Based on these results and previous work we suggest that destabilization of the semireduced quinone, facilitates a light-induced damage in D 1 which triggers its degradation. 
  Reference    Z. Naturforsch. 45c, 402—408 (1990); received November 21 1989 
  Published    1990 
  Keywords    Herbicide Resistance, Thermoluminescence, D 1 Turnover, Synechococcus PCC 7942 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0402.pdf 
 Identifier    ZNC-1990-45c-0402 
 Volume    45 
2Author    Susana Shochata, Noam Adira, Alma Gala, Yorinao Inoueb, Laurence Metsc, Itzhak OhadaRequires cookie*
 Title    Photoinactivation of Photosystem II and Degradation of the D 1 Protein are Reduced in a Cytochrome b j f -Less Mutant of Chlamydomonas reinhardtii  
 Abstract    The effect of unoccupancy of the Q B site by plastoquinone on the photoinactivation of reac­ tion center II in a Cyt b jf-less mutant of Chlamydomonas reinhardtii, Bb, was investigated. In these cells the oxidation of plastoquinol generated by electron flow via RC II to plastoquinone and thus the turnover of PQH2/PQ via the Q B site are drastically reduced. Reaction center II of the mutant cells was resistant to photoinactivation relative to the control cells as demonstrated by measurements of light-induced destabilization of S2-QB charge recombination, rise in in­ trinsic fluorescence and loss of variable fluorescence. These parameters relate to functions in­ volving the reaction center II D 1 protein. The light-induced degradation of D 1 in the mutant cells was also considerably reduced, with a ;l/ 2 value of 7 h as compared, under similar condi­ tions, to about 1.5 h for the control cells. These results indicate that the photoinactivation of RC II and turnover of the D 1 protein are related and require occupancy of the Q B site by PQ and its light-driven reduction. 
  Reference    Z. Naturforsch. 45c, 395—401 (1990); received November 24 1989 
  Published    1990 
  Keywords    Cytochrome b j f, Chlamydomonas, D 1 Turnover, Q B, Thermoluminescence, Photoinhibition 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0395.pdf 
 Identifier    ZNC-1990-45c-0395 
 Volume    45