pH dependence of the four individual transitions in the catalytic S-cycle during photosynthetic oxygen evolution.
(2002) In Biochemistry 41(18). p.5830-5843- Abstract
- We have investigated the pH dependence for each individual redox transition in the S-cycle of the oxygen evolving complex (OEC) of photosystem II by electron paramagnetic resonance (EPR) spectroscopy. In the experiments, OEC is advanced to the appropriate S-state at normal pH. Then, the pH is rapidly changed, and a new flash is given. The ability to advance to the next S-state in the cycle at different pHs is determined by measurements of the decrease or increase of characteristic EPR signals from the OEC in different S-states. In some cases the measured EPR signals are very small (this holds especially for the S0 ML signal at pH >7.5 and pH <4.8). Therefore, we refrain from providing error limits for the determined pK's. Our results... (More)
- We have investigated the pH dependence for each individual redox transition in the S-cycle of the oxygen evolving complex (OEC) of photosystem II by electron paramagnetic resonance (EPR) spectroscopy. In the experiments, OEC is advanced to the appropriate S-state at normal pH. Then, the pH is rapidly changed, and a new flash is given. The ability to advance to the next S-state in the cycle at different pHs is determined by measurements of the decrease or increase of characteristic EPR signals from the OEC in different S-states. In some cases the measured EPR signals are very small (this holds especially for the S0 ML signal at pH >7.5 and pH <4.8). Therefore, we refrain from providing error limits for the determined pK's. Our results indicate that the S1 --> S2 transition is independent of pH between 4.1 and 8.4. All other S-transitions are blocked at low pH. In the acidic region, the pK's for the inhibition of the S2 --> S3, the S3 --> [S4] --> S0, and the S0 --> S1 transitions are about 4.0, 4.5, and 4.7, respectively. The similarity of these pK values indicates that the inhibition of the steady-state oxygen evolution in the acidic range, which occurs with pK approximately 4.8, is a consequence of similar pH blocks in three of the redox steps involved in the oxygen evolution. In the alkaline region, we report a clear pH block in the S3 --> [S4] --> S0 transition with a pK of about 8.0. Our study also indicates the existence of a pH block at very high pH (pK approximately 9.4) in the S2 --> S3 transition. The S0 --> S1 transition is not affected, at least up to pH 9.0. This suggests that the inhibition of the steady-state oxygen evolution, which occurs with a pK of 8.0, is dominated by the inhibition of the S3 --> [S4] --> S0 transition. Our results are obtained in the presence of 5% methanol (v/v). However, it is unlikely that the determined pK's are affected by the presence of methanol since our results also show that the pH dependence of the steady-state oxygen evolution is not affected by methanol. The results in the alkaline region are in good agreement with a model, which suggests that the redox potential of Y(Z*)/Y(Z) is directly affected by high pH. At high pH the Y(Z*)/Y(Z) potential becomes lower than that of S2/S1 and S3/S2. The acidic block, with a pK of 4-5 in three S-transitions, implies that the inhibition mechanism is similar, and we suggest that it reflects protonation of a carboxylic side chain in the proton relay that expels protons from the OEC. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/107903
- author
- Bernat, Gabor LU ; Morvaridi, Susan F LU ; Feyziyev, Yashar LU and Styring, Stenbjörn LU
- organization
- publishing date
- 2002
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Catalysis, Hydrogen-Ion Concentration, Oxidation-Reduction, Oxygen : metabolism, Photosynthesis, Photosynthetic Reaction Center, Plant : chemistry, Plant : metabolism, Protons, Spinach : metabolism, Electron Spin Resonance Spectroscopy
- in
- Biochemistry
- volume
- 41
- issue
- 18
- pages
- 5830 - 5843
- publisher
- The American Chemical Society (ACS)
- external identifiers
-
- wos:000175365300015
- pmid:11980487
- scopus:0037035522
- ISSN
- 0006-2960
- DOI
- 10.1021/bi011691u
- language
- English
- LU publication?
- yes
- id
- b66be7ce-d57f-4f42-9b49-ee8fb072f0d5 (old id 107903)
- date added to LUP
- 2016-04-01 12:19:33
- date last changed
- 2022-04-21 05:53:38
@article{b66be7ce-d57f-4f42-9b49-ee8fb072f0d5, abstract = {{We have investigated the pH dependence for each individual redox transition in the S-cycle of the oxygen evolving complex (OEC) of photosystem II by electron paramagnetic resonance (EPR) spectroscopy. In the experiments, OEC is advanced to the appropriate S-state at normal pH. Then, the pH is rapidly changed, and a new flash is given. The ability to advance to the next S-state in the cycle at different pHs is determined by measurements of the decrease or increase of characteristic EPR signals from the OEC in different S-states. In some cases the measured EPR signals are very small (this holds especially for the S0 ML signal at pH >7.5 and pH <4.8). Therefore, we refrain from providing error limits for the determined pK's. Our results indicate that the S1 --> S2 transition is independent of pH between 4.1 and 8.4. All other S-transitions are blocked at low pH. In the acidic region, the pK's for the inhibition of the S2 --> S3, the S3 --> [S4] --> S0, and the S0 --> S1 transitions are about 4.0, 4.5, and 4.7, respectively. The similarity of these pK values indicates that the inhibition of the steady-state oxygen evolution in the acidic range, which occurs with pK approximately 4.8, is a consequence of similar pH blocks in three of the redox steps involved in the oxygen evolution. In the alkaline region, we report a clear pH block in the S3 --> [S4] --> S0 transition with a pK of about 8.0. Our study also indicates the existence of a pH block at very high pH (pK approximately 9.4) in the S2 --> S3 transition. The S0 --> S1 transition is not affected, at least up to pH 9.0. This suggests that the inhibition of the steady-state oxygen evolution, which occurs with a pK of 8.0, is dominated by the inhibition of the S3 --> [S4] --> S0 transition. Our results are obtained in the presence of 5% methanol (v/v). However, it is unlikely that the determined pK's are affected by the presence of methanol since our results also show that the pH dependence of the steady-state oxygen evolution is not affected by methanol. The results in the alkaline region are in good agreement with a model, which suggests that the redox potential of Y(Z*)/Y(Z) is directly affected by high pH. At high pH the Y(Z*)/Y(Z) potential becomes lower than that of S2/S1 and S3/S2. The acidic block, with a pK of 4-5 in three S-transitions, implies that the inhibition mechanism is similar, and we suggest that it reflects protonation of a carboxylic side chain in the proton relay that expels protons from the OEC.}}, author = {{Bernat, Gabor and Morvaridi, Susan F and Feyziyev, Yashar and Styring, Stenbjörn}}, issn = {{0006-2960}}, keywords = {{Catalysis; Hydrogen-Ion Concentration; Oxidation-Reduction; Oxygen : metabolism; Photosynthesis; Photosynthetic Reaction Center; Plant : chemistry; Plant : metabolism; Protons; Spinach : metabolism; Electron Spin Resonance Spectroscopy}}, language = {{eng}}, number = {{18}}, pages = {{5830--5843}}, publisher = {{The American Chemical Society (ACS)}}, series = {{Biochemistry}}, title = {{pH dependence of the four individual transitions in the catalytic S-cycle during photosynthetic oxygen evolution.}}, url = {{http://dx.doi.org/10.1021/bi011691u}}, doi = {{10.1021/bi011691u}}, volume = {{41}}, year = {{2002}}, }