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pH dependent competition between YZ and YD in photosystem II probed by illumination at 5 K

Havelius, Kajsa G.V. LU and Styring, Stenbjörn LU (2007) In Biochemistry 46(26). p.7865-7874
Abstract

The photosystem II (PSII) reaction center contains two redox active tyrosines, YZ and YD, situated on the D1 and D2 proteins, respectively. By illumination at 5 K, oxidation of YZ in oxygen-evolving PSII can be observed as induction of the Split S1 EPR signal from YZ• in magnetic interaction with the CaMn4 cluster, whereas oxidation of YD can be observed as the formation of the free radical EPR signal from YD •. We have followed the light induced induction at 5 K of the Split S1 signal between pH 4-8.5. The formation of the signal, that is, the oxidation of YZ, is pH independent and efficient between pH 5.5... (More)

The photosystem II (PSII) reaction center contains two redox active tyrosines, YZ and YD, situated on the D1 and D2 proteins, respectively. By illumination at 5 K, oxidation of YZ in oxygen-evolving PSII can be observed as induction of the Split S1 EPR signal from YZ• in magnetic interaction with the CaMn4 cluster, whereas oxidation of YD can be observed as the formation of the free radical EPR signal from YD •. We have followed the light induced induction at 5 K of the Split S1 signal between pH 4-8.5. The formation of the signal, that is, the oxidation of YZ, is pH independent and efficient between pH 5.5 and 8.5. At low pH, the split signal formation decreases with pKa ∼4.7-4.9. In samples with chemically pre-reduced YD, the pH dependent competition between YZ and YD was studied. Only YZ was oxidized below pH 7.2, but at pH above 7.2, the oxidation of YD became possible, and the formation of the Split S1 signal diminished. The onset of YD oxidation occurred with pK a ∼8.0, while the Split S1 signal decreased with pKa ∼7.9 demonstrating that the two tyrosines compete in this pH interval. The results reflect the formation and breaking of hydrogen bonds between YZ and D1-His190 (HisZ) and YD and D2-His190 (HisD), respectively. The oxidation of respective tyrosine at 5 K demands that the hydrogen bond is well-defined; otherwise, the low-temperature oxidation is not possible. The results are discussed in the framework of recent literature data and with respect to the different oxidation kinetics of YZ and YD.

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author
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publishing date
type
Contribution to journal
publication status
published
in
Biochemistry
volume
46
issue
26
pages
10 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • pmid:17559194
  • scopus:34347386893
ISSN
0006-2960
DOI
10.1021/bi700377g
language
English
LU publication?
no
id
dde50cfa-8a25-44e0-98d1-f71b47e2ffa8
date added to LUP
2020-01-15 10:35:00
date last changed
2024-10-02 20:17:49
@article{dde50cfa-8a25-44e0-98d1-f71b47e2ffa8,
  abstract     = {{<p>The photosystem II (PSII) reaction center contains two redox active tyrosines, Y<sub>Z</sub> and Y<sub>D</sub>, situated on the D1 and D2 proteins, respectively. By illumination at 5 K, oxidation of Y<sub>Z</sub> in oxygen-evolving PSII can be observed as induction of the Split S<sub>1</sub> EPR signal from Y<sub>Z</sub><sup>•</sup> in magnetic interaction with the CaMn<sub>4</sub> cluster, whereas oxidation of Y<sub>D</sub> can be observed as the formation of the free radical EPR signal from Y<sub>D</sub> <sup>•</sup>. We have followed the light induced induction at 5 K of the Split S<sub>1</sub> signal between pH 4-8.5. The formation of the signal, that is, the oxidation of Y<sub>Z</sub>, is pH independent and efficient between pH 5.5 and 8.5. At low pH, the split signal formation decreases with pK<sub>a</sub> ∼4.7-4.9. In samples with chemically pre-reduced Y<sub>D</sub>, the pH dependent competition between Y<sub>Z</sub> and Y<sub>D</sub> was studied. Only Y<sub>Z</sub> was oxidized below pH 7.2, but at pH above 7.2, the oxidation of Y<sub>D</sub> became possible, and the formation of the Split S<sub>1</sub> signal diminished. The onset of Y<sub>D</sub> oxidation occurred with pK <sub>a</sub> ∼8.0, while the Split S<sub>1</sub> signal decreased with pK<sub>a</sub> ∼7.9 demonstrating that the two tyrosines compete in this pH interval. The results reflect the formation and breaking of hydrogen bonds between Y<sub>Z</sub> and D1-His190 (His<sub>Z</sub>) and Y<sub>D</sub> and D2-His190 (His<sub>D</sub>), respectively. The oxidation of respective tyrosine at 5 K demands that the hydrogen bond is well-defined; otherwise, the low-temperature oxidation is not possible. The results are discussed in the framework of recent literature data and with respect to the different oxidation kinetics of Y<sub>Z</sub> and Y<sub>D</sub>.</p>}},
  author       = {{Havelius, Kajsa G.V. and Styring, Stenbjörn}},
  issn         = {{0006-2960}},
  language     = {{eng}},
  month        = {{07}},
  number       = {{26}},
  pages        = {{7865--7874}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Biochemistry}},
  title        = {{pH dependent competition between Y<sub>Z</sub> and Y<sub>D</sub> in photosystem II probed by illumination at 5 K}},
  url          = {{http://dx.doi.org/10.1021/bi700377g}},
  doi          = {{10.1021/bi700377g}},
  volume       = {{46}},
  year         = {{2007}},
}