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pH dependence of th...
pH dependence of the four individual transitions in the catalytic S-cycle during photosynthetic oxygen evolution.
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- Bernat, Gabor (författare)
- Lund University,Lunds universitet,Biokemi och Strukturbiologi,Centrum för Molekylär Proteinvetenskap,Kemiska institutionen,Institutioner vid LTH,Lunds Tekniska Högskola,Biochemistry and Structural Biology,Center for Molecular Protein Science,Department of Chemistry,Departments at LTH,Faculty of Engineering, LTH
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- Morvaridi, Susan F (författare)
- Lund University,Lunds universitet,Biokemi och Strukturbiologi,Centrum för Molekylär Proteinvetenskap,Kemiska institutionen,Institutioner vid LTH,Lunds Tekniska Högskola,Biochemistry and Structural Biology,Center for Molecular Protein Science,Department of Chemistry,Departments at LTH,Faculty of Engineering, LTH
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- Feyziyev, Yashar (författare)
- Lund University,Lunds universitet,Biokemi och Strukturbiologi,Centrum för Molekylär Proteinvetenskap,Kemiska institutionen,Institutioner vid LTH,Lunds Tekniska Högskola,Biochemistry and Structural Biology,Center for Molecular Protein Science,Department of Chemistry,Departments at LTH,Faculty of Engineering, LTH
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- Styring, Stenbjörn (författare)
- Lund University,Lunds universitet,Biokemi och Strukturbiologi,Centrum för Molekylär Proteinvetenskap,Kemiska institutionen,Institutioner vid LTH,Lunds Tekniska Högskola,Biochemistry and Structural Biology,Center for Molecular Protein Science,Department of Chemistry,Departments at LTH,Faculty of Engineering, LTH
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(creator_code:org_t)
- 2002-04-11
- 2002
- Engelska.
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Ingår i: Biochemistry. - : American Chemical Society (ACS). - 0006-2960 .- 1520-4995. ; 41:18, s. 5830-5843
- Relaterad länk:
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http://dx.doi.org/10...
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https://lup.lub.lu.s...
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https://doi.org/10.1...
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Abstract
Ämnesord
Stäng
- 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.
Ämnesord
- NATURVETENSKAP -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)
- NATURAL SCIENCES -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)
Nyckelord
- Catalysis
- Hydrogen-Ion Concentration
- Oxidation-Reduction
- Oxygen : metabolism
- Photosynthesis
- Photosynthetic Reaction Center
- Plant : chemistry
- Plant : metabolism
- Protons
- Spinach : metabolism
- Electron Spin Resonance Spectroscopy
Publikations- och innehållstyp
- art (ämneskategori)
- ref (ämneskategori)
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