Release of oxidized plastocyanin from photosystem I limits electron transfer between photosystem I and cytochrome b6f complex in vivo.
We used fast absorbance spectroscopy to investigate in vivo binding dynamics and electron transfer between plastocyanin (pc) and photosystem I (PSI), and cytochrome (cyt) f oxidation kinetics in Chlamydomonas reinhardtii mutants in which either the binding or the release of pc from PSI was diminished. Under single flash-excitation conditions, electron flow between PSI and the cyt complex was not affected by a 5-fold lowering of the binding affinity of pc to PSI, as induced by a mutation replacing the tryptophan-651 of the PsaA subunit by a serine residue (PsaA-W651S). On the other hand, electron flow from PSI to the cyt b(6)f complex was very sensitive to a 2- to 3-fold decrease in the rate of pc release from PSI, obtained by replacing the glutamic acid residue 613 of the PsaB subunit with glutamine (PsaB-E613N). Thus, our data indicate that under these experimental conditions the release of oxidized pc limits electron transfer between cyt b(6)f complex and PSI in vivo.
Finazzi
Giovanni
G
Unité Mixte de Recherche 7141 Centre National de la Recherche Scientifique, Institut de Biologie Physico-Chimique, 75005 Paris, France. giovanni.finazzi@ibpc.fr
Sommer
Frederik
F
Hippler
Michael
M
D000818:Animals; D001665:Binding Sites; D002696:Chlamydomonas; D045346:Cytochrome b6f Complex / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D018698:Glutamic Acid / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry; D007700:Kinetics; D009154:Mutation; D009249:NADP / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D010641:Phenotype; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D010970:Plastocyanin / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D012694:Serine / Q000737:chemistry; D013053:Spectrophotometry; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry
D045331:Photosystem I Protein Complex; C089909:photosystem I, psaB subunit; D005973:Glutamine; D018698:Glutamic Acid; D012694:Serine; D009249:NADP; D014364:Tryptophan; D010970:Plastocyanin; D045346:Cytochrome b6f Complex; D010100:Oxygen