Photosystem II in a mutant of Chlamydomonas reinhardtii lacking the 23 kDa psbP protein shows increased sensitivity to photoinhibition in the absence of chloride |
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Authors: | Maria Rova Lars-Gunnar Franzén Per-Olof Fredriksson Stenbjörn Styring |
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Affiliation: | (1) Department of Chemistry, University of Karlstad, Box 9501, S-650 09 Karlstad, Sweden;(2) Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, S-106 91 Stockholm, Sweden |
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Abstract: | The psbP gene product, the so called 23 kDa extrinsic protein, is involved in water oxidation carried out by Photosystem II. However, the protein is not absolutely required for water oxidation. Here we have studied Photosystem II mediated electron transfer in a mutant of Chlamydomonas reinhardtii, the FUD 39 mutant, that lacks the psbP protein. When grown in dim light the Photosystem II content in thylakoid membranes of FUD 39 is approximately similar to that in the wild-type. The oxygen evolution is dependent on the presence of chloride as a cofactor, which activates the water oxidation with a dissociation constant of about 4 mM. In the mutant, the oxygen evolution is very sensitive to photoinhibition when assayed at low chloride concentrations while chloride protects against photoinhibition with a dissociation constant of about 5 mM. The photoinhibition is irreversible as oxygen evolution cannot be restored by the addition of chloride to inhibited samples. In addition the inhibition seems to be targeted primarily to the Mn-cluster in Photosystem II as the electron transfer through the remaining part of Photosystem II is photoinhibited with slower kinetics. Thus, this mutant provides an experimental system in which effects of photoinhibition induced by lesions at the donor side of Photosystem II can be studied in vivo.Abbreviations Chl chlorophyll - DCIP 2,6-dichlorophenolindophenol - DPC 2,2-diphenylcarbonic dihydrazide - HEPES 4-(2-hydroxyethyl)-1-piperazinethanesulfonic acid - P680 the primary electron donor to PS II - PpBQ phenyl-p-benzoquinone - PS II Photosystem II - QA the first quinone acceptor of PS II - QB the second quinone acceptor of PS II - SDS sodium dodecyl sulfate - Tris tris(hydroxymethyl)aminomethane - TyrD accessory electron donor on the D2-protein - TyrZ tyrosine residue, acting as electron carrier between P680 and the water oxidizing system |
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Keywords: | Chlamydomonas chloride OEE2 protein photoinhibition Photosystem II psbP gene |
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