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

► The lumen-exposed domain of photosystem I subunit PsaF, a target of thioredoxin. ► The binding of plastocyanin to PsaF becomes weaker upon reduction (thiolation) of PsaF. ► Oxidized plastocyanin facilitates oxidation of cystein thiols and formation of disulphide bridge in PsaF. ► Example of thioredoxin-mediated reduction and inactivation within the lumen. ► Reactivation through oxidation of the thiolated form of PsaF.