Copper effect on the protein composition of photosystem II

electron donor of photosystem II reaction centre; PFD, photon flux density; Pheo, pheophytin; PS, photosystem; QA and QB, primary and secondary plastoquinone electron acceptors of photosystem II; RC, reaction centre; SDS, sodium dodecyl sulphate; Tyrz tyrosine 161 of the D1 polypeptide of photosystem II. We provide data from in vitro experiment on the polypeptide composition, photosynthetic electron transport and oxygen evolution activity of intact photosystem II (PSII) preparations under Cu(II) toxicity conditions. Low Cu(II) concentrations (Cu(II) per PSII reaction centre unit < 230) that caused around 50 % inhibition of variable chlorophyll a fluorescence and oxygen evolution activity did not affect the polypeptide composition of PSII. However, the extrinsic proteins of 33, 24 and 17 kDa of the oxygen-evolving complex of PSII were removed when samples were treated with 300 μM CuCl2 (Cu(II) per PSII reaction centre unit = 1400). The LHCII antenna complex and D1 protein of the reaction centre of PSII were not affected at these Cu(II) concentrations. The results indicated that the initial inhibition of the PSII electron transport and oxygen-evolving activity induced by the presence of toxic Cu(II) concentrations occurred before the damage of the oxygen-evolving complex. Indeed, more than 50 % inhibition could be achieved in conditions where its protein composition and integrity was apparently preserved