Photoinactivation of photosystem II and degradation of the D 1 protein are reduced in a cytochrome b6/f-less mutant of Chlamydomonas reinhardtii.
The effect of unoccupancy of the QB site by plastoquinone on the photoinactivation of reaction center II in a Cyt b6/f-less mutant of Chlamydomonas reinhardtii, B6, 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 QB 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 intrinsic fluorescence and loss of variable fluorescence. These parameters relate to functions involving the reaction center II D 1 protein. The light-induced degradation of D 1 in the mutant cells was also considerably reduced, with a t1/2 value of 7 h as compared, under similar conditions, 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 QB site by PQ and its light-driven reduction.
Department of Biological Chemistry, Hebrew University of Jerusalem, Israel.
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Shochat
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Adir
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Gal
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Inoue
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Mets
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Ohad
D002696:Chlamydomonas / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects; D003573:Cytochrome b Group / Q000235:genetics*; D045346:Cytochrome b6f Complex; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D009154:Mutation; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000528:radiation effects
D003573:Cytochrome b Group; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D045346:Cytochrome b6f Complex