Inhibition of tyrosine Z photooxidation after formation of the S3 state in Ca(2+)-depleted and Cl(-)-depleted photosystem II.
Ca2+ and Cl- are obligatory cofactors in photosystem II (PS-II), the oxygen-evolving enzyme of plants. The sites of inhibition in both Ca(2+)- and Cl(-)-depleted PS-II were compared using EPR and flash absorption spectroscopies to follow the extent of the photooxidation of the redox-active tyrosine (TyrZ) and of the primary electron donor chlorophyll (P680) and their subsequent reduction in the dark. The inhibition occurred after formation of the S3 state in Ca(2+)-depleted PS-II. In Cl(-)-depleted photosystem II, the inhibition occurred after formation of the S3 state in about half of the centers and probably after S2TyrZ+ formation in the remaining centers. After the S3 state was formed in Ca(2+)- and Cl(-)-depleted photosystem II, electron transfer from TyrZ to P680 was inhibited. This inhibition is discussed in terms of electrostatic constraints resulting from S3 formation in the absence of Ca2+ and Cl-.
Boussac
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A
Service de Bioénergétique (URA CNRS 1290), Gif sur Yvette, France.
Sétif
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Rutherford
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AW
D002021:Buffers; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002712:Chlorides / Q000737:chemistry / Q000378:metabolism*; D003080:Cold Temperature; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D007700:Kinetics; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D045332:Photosystem II Protein Complex; D013057:Spectrum Analysis; D014443:Tyrosine / Q000737:chemistry*
D002021:Buffers; D002712:Chlorides; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D014443:Tyrosine; D002118:Calcium