Thioredoxin-mediated reduction of the photosystem I subunit PsaF and activation through oxidation by the interaction partner plastocyanin

In the photosynthetic electron-transfer chain, the photosystem I subunit PsaF is involved in the specific binding of plastocyanin. Using fluorescence electrophoresis we show here that the luminal domain of PsaF is a target for thioredoxin-mediated reduction of the Cys residues 8 and 63. Furthermore, by using NMR spectroscopy, we show that the thiolated form of PsaF has a lower affinity towards reduced plastocyanin than when the disulfide bridge is intact. Time-resolved absorbance measurements and fluorescence electrophoresis shows that oxidized plastocyanin can re-oxidize PsaF and thus restore the active form.