Elevation of photosystem II thermal stability at pH 5.7 due to the structural transition in the oxygen-evolving complex

In the presented work, a comparative study of the photosystem II (PSII) preparations resistance to elevated temperatures at pH 6.5 and 5.7 was carried out. The native and Ca-depleted PSII are completely inactivated (oxygen evolution and 2,6-dichlorophenolindophenol reduction) at 50 degrees C in buffer with pH 6.5. Inactivation is determined mainly by destruction of manganese cluster in the oxygen-evolving complex (OEC) since the electron-transport chain in the Mn-depleted PSII is more resistant to the heat treatment. We found that PSII membranes suspended in buffer with pH 5.7 are less sensitive to heat stress (50 degrees C) than the samples at pH 6.5. Residual rate of electron transport was about 22% and 3% respectively after heat treatment. We suggest that the increasing of the OEC resistance to the heat stress at pH 5.7 is determined by a pH-dependent change of the OEC manganese cations redox potential.

Automated summary

This study compared the resistance of photosystem II (PSII) preparations to elevated temperatures at pH 6.5 and 5.7. The findings show that PSII membranes suspended in buffer with pH 5.7 are less sensitive to heat stress compared to samples at pH 6.5, potentially due to a pH-dependent change in the OEC manganese cations redox potential.