scholarly journals Proton Coupled Electron Transfer and Redox-Active Tyrosine Z in the Photosynthetic Oxygen-Evolving Complex

2011 ◽  
Vol 133 (29) ◽  
pp. 11084-11087 ◽  
Author(s):  
James M. Keough ◽  
David L. Jenson ◽  
Ashley N. Zuniga ◽  
Bridgette A. Barry
Keyword(s):  
Electron Transfer ◽  
Oxygen Evolving Complex ◽  
Proton Coupled Electron Transfer ◽  
Redox Active ◽  
Tyrosine Z ◽  
Photosynthetic Oxygen ◽  
Oxygen Evolving

Proton-Coupled Electron Transfer During the S-State Transitions of the Oxygen-Evolving Complex of Photosystem II

2015 ◽  
Vol 119 (24) ◽  
pp. 7366-7377 ◽  
Author(s):  
Muhamed Amin ◽  
Leslie Vogt ◽  
Witold Szejgis ◽  
Serguei Vassiliev ◽  
Gary W. Brudvig ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Photosystem Ii ◽  
State Transitions ◽  
Oxygen Evolving Complex ◽  
Proton Coupled Electron Transfer ◽  
Oxygen Evolving

scholarly journals Calcium, conformational selection, and redox-active tyrosine YZ in the photosynthetic oxygen-evolving cluster

2018 ◽  
Vol 115 (22) ◽  
pp. 5658-5663 ◽  
Author(s):  
Zhanjun Guo ◽  
Jiayuan He ◽  
Bridgette A. Barry
Keyword(s):  
Metal Cluster ◽  
Bound Water ◽  
Tyrosyl Radical ◽  
Calcium Dependent ◽  
Proton Coupled Electron Transfer ◽  
Redox Active ◽  
Bonding Interaction ◽  
Photosynthetic Oxygen ◽  
Radical Transfer ◽  
Oxygen Evolving

In Photosystem II (PSII), YZ (Tyr161D1) participates in radical transfer between the chlorophyll donor and the Mn4CaO5 cluster. Under flashing illumination, the metal cluster cycles among five Sn states, and oxygen is evolved from water. The essential YZ is transiently oxidized and reduced on each flash in a proton-coupled electron transfer (PCET) reaction. Calcium is required for function. Of reconstituted divalent ions, only strontium restores oxygen evolution. YZ is predicted to hydrogen bond to calcium-bound water and to His190D1 in PSII structures. Here, we report a vibrational spectroscopic study of YZ radical and singlet in the presence of the metal cluster. The S2 state is trapped by illumination at 190 K; flash illumination then generates the S2YZ radical. Using reaction-induced FTIR spectroscopy and divalent ion depletion/substitution, we identify calcium-sensitive tyrosyl radical and tyrosine singlet bands in the S2 state. In calcium-containing PSII, two CO stretching bands are detected at 1,503 and 1,478 cm−1. These bands are assigned to two different radical conformers in calcium-containing PSII. At pH 6.0, the 1,503-cm−1 band shifts to 1,507 cm−1 in strontium-containing PSII, and the band is reduced in intensity in calcium-depleted PSII. These effects are consistent with a hydrogen-bonding interaction between the calcium site and one conformer of radical YZ. Analysis of the amide I region indicates that calcium selects for a PCET reaction in a subset of the YZ conformers, which are trapped in the S2 state. These results support the interpretation that YZ undergoes a redox-coupled conformational change, which is calcium dependent.

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