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The S3 State of the Oxygen-Evolving Complex in Photosystem II Is Converted to the S2YZ State at Alkaline pH

Geijer, Paulina LU ; Morvaridi, Susan F LU and Styring, Stenbjörn LU (2001) In Biochemistry 40(36). p.10881-10891
Abstract
Here we report an EPR signal that is induced by a pH jump to alkaline pH in the S3 state of the oxygen-evolving complex in photosystem II. The S3 state is first formed with two flashes at pH 6. Thereafter, the pH is changed in the dark prior to freezing of the sample. The EPR signal is 90-100 G wide and centered around g = 2. The signal is reversibly induced with a pK = 8.5 ± 0.3 and is very stable with a decay half-time of 5-6 min. If the pH is changed in the dark from pH 8.6 to 6.0, the signal disappears although the S3 state remains. We propose that the signal arises from the interaction between the Mn cluster and YZ, resulting in the spin-coupled S2YZ signal. Our data suggest that the potential of the YZ/YZ redox couple is sensitive to... (More)
Here we report an EPR signal that is induced by a pH jump to alkaline pH in the S3 state of the oxygen-evolving complex in photosystem II. The S3 state is first formed with two flashes at pH 6. Thereafter, the pH is changed in the dark prior to freezing of the sample. The EPR signal is 90-100 G wide and centered around g = 2. The signal is reversibly induced with a pK = 8.5 ± 0.3 and is very stable with a decay half-time of 5-6 min. If the pH is changed in the dark from pH 8.6 to 6.0, the signal disappears although the S3 state remains. We propose that the signal arises from the interaction between the Mn cluster and YZ, resulting in the spin-coupled S2YZ signal. Our data suggest that the potential of the YZ/YZ redox couple is sensitive to the ambient pH in the S3 state. The alkaline pH decreases the potential of the YZ/YZ couple so that YZ can give back an electron to the S3 state, thereby obtaining the S2YZ EPR signal. The tyrosine oxidation also involves proton release from YZ, and the results support a mechanism where this proton is released to the bulk medium presumably via a close-lying base. Thus, the equilibrium is changed from S3YZ to S2YZ by the alkaline pH. At normal pH (pH 5.5-7), this equilibrium is set strongly to the S3YZ state. The results are discussed in relation to the present models of water oxidation. Consequences for the relative redox potentials of YZ/YZ and S3/S2 at different pH values are discussed. We also compare the pH-induced S2YZ signal with the S2YZ signal from Ca2+-depleted photosystem II. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Biochemistry
volume
40
issue
36
pages
10881 - 10891
publisher
The American Chemical Society
external identifiers
  • scopus:0035845651
ISSN
0006-2960
DOI
10.1021/bi010040v
language
English
LU publication?
yes
id
faa51570-70ea-409b-9c70-2ce0250d8853 (old id 124966)
date added to LUP
2007-07-04 17:03:35
date last changed
2018-05-29 11:32:56
@article{faa51570-70ea-409b-9c70-2ce0250d8853,
  abstract     = {Here we report an EPR signal that is induced by a pH jump to alkaline pH in the S3 state of the oxygen-evolving complex in photosystem II. The S3 state is first formed with two flashes at pH 6. Thereafter, the pH is changed in the dark prior to freezing of the sample. The EPR signal is 90-100 G wide and centered around g = 2. The signal is reversibly induced with a pK = 8.5 ± 0.3 and is very stable with a decay half-time of 5-6 min. If the pH is changed in the dark from pH 8.6 to 6.0, the signal disappears although the S3 state remains. We propose that the signal arises from the interaction between the Mn cluster and YZ, resulting in the spin-coupled S2YZ signal. Our data suggest that the potential of the YZ/YZ redox couple is sensitive to the ambient pH in the S3 state. The alkaline pH decreases the potential of the YZ/YZ couple so that YZ can give back an electron to the S3 state, thereby obtaining the S2YZ EPR signal. The tyrosine oxidation also involves proton release from YZ, and the results support a mechanism where this proton is released to the bulk medium presumably via a close-lying base. Thus, the equilibrium is changed from S3YZ to S2YZ by the alkaline pH. At normal pH (pH 5.5-7), this equilibrium is set strongly to the S3YZ state. The results are discussed in relation to the present models of water oxidation. Consequences for the relative redox potentials of YZ/YZ and S3/S2 at different pH values are discussed. We also compare the pH-induced S2YZ signal with the S2YZ signal from Ca2+-depleted photosystem II.},
  author       = {Geijer, Paulina and Morvaridi, Susan F and Styring, Stenbjörn},
  issn         = {0006-2960},
  language     = {eng},
  number       = {36},
  pages        = {10881--10891},
  publisher    = {The American Chemical Society},
  series       = {Biochemistry},
  title        = {The S3 State of the Oxygen-Evolving Complex in Photosystem II Is Converted to the S2YZ State at Alkaline pH},
  url          = {http://dx.doi.org/10.1021/bi010040v},
  volume       = {40},
  year         = {2001},
}