Trichloroacetate Affects the Redox Active Tyrosine 160 of the D2 Polypeptide of the Photosystem II Core

Trichloroacetate (TCA) affects the redox property of YD (tyrosine-160 on D2 polypeptide) after the removal of 33 kDa extrinsic polypeptide from the photosystem II (PSII) core. However, TCA has no obvious effect on the redox property of YZ , confirming that the environments around YZ and YD are quite different. The conclusion on the effects on YD is based primarily on the observation that Y D+ is not detected as the EPR signal IIslow when 33 kDa polypeptide is released by TCA -treatment. Dialysis of the TCA -treated sample that allows the rebinding of mostly 33 kDa polypeptide restores Y D+, showing that the loss of the EPR signal IIslow| takes place after the removal of 33 kD a polypeptide but not the release of manganese (Mn). Additionally, treatment of several halogenated acetates on Tris-washed PSII particles shows that the degree of their effects on suppressing EPR signal IIslow is correlated with their hydrophobicity. It is postulated that Y D becomes more accessible to some small hydrophobic molecules depending upon their hydrophobicity when 33 kDa poly­peptide is removed.