Abstract
Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and functional roles in active photosystem II are still a matter of debate. We have investigated this issue by studying the effects of Cl- replacement by Br- in active PSII. In Br- substituted samples, Cl- is effectively replaced by Br- in the presence of 1.2M NaBr under room light with protection of anaerobic atmosphere followed by dialysis. The following results have been obtained. i) The oxygen-evolving activities of the Br--PSII samples are significantly lower than that of the Cl--PSII samples; ii) The same S2 multiline EPR signals are observed in both Br- and Cl--PSII samples; iii) The amplitudes of the visible light induced S1TyrZ• and S2TyrZ• EPR signals are significantly decreased after Br- substitution; the S1TyrZ• EPR signal is up-shifted about 8G, whereas the S2TyrZ• signal is down-shifted about 12G after Br- substitution. These results imply that the redox properties of TyrZ and spin interactions between TyrZ• and Mn-cluster could be significantly modified due to Br- substitution. It is suggested that Cl-/Br- probably coordinates to the Ca2+ ion of the Mn-cluster in active photosystem II.
Original language | English (US) |
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Pages (from-to) | 1421-1427 |
Number of pages | 7 |
Journal | Biochimica et Biophysica Acta - Bioenergetics |
Volume | 1797 |
Issue number | 8 |
DOIs | |
State | Published - Aug 2010 |
Externally published | Yes |
Keywords
- Bromide substitution
- Chloride
- Electron paramagnetic resonance
- Mn-cluster
- Photosystem II
- Tyrosine Z