pH dependence of the four individual transitions in the catalytic S-cycle during photosynthetic oxygen evolution.

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Bernat, GaborLund 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 (författare)

pH dependence of the four individual transitions in the catalytic S-cycle during photosynthetic oxygen evolution.

Artikel/kapitelEngelska2002

Förlag, utgivningsår, omfång ...

2002-04-11
American Chemical Society (ACS),2002

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LIBRIS-ID:oai:lup.lub.lu.se:b66be7ce-d57f-4f42-9b49-ee8fb072f0d5
https://lup.lub.lu.se/record/107903URI
https://doi.org/10.1021/bi011691uDOI

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Språk:engelska
Sammanfattning på:engelska

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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 och genrebeteckningar

NATURVETENSKAP Biologi Biokemi och molekylärbiologi hsv//swe
NATURAL SCIENCES Biological Sciences Biochemistry and Molecular Biology hsv//eng
Catalysis
Hydrogen-Ion Concentration
Oxidation-Reduction
Oxygen : metabolism
Photosynthesis
Photosynthetic Reaction Center
Plant : chemistry
Plant : metabolism
Protons
Spinach : metabolism
Electron Spin Resonance Spectroscopy

Biuppslag (personer, institutioner, konferenser, titlar ...)

Morvaridi, Susan FLund 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(Swepub:lu)biok-fmo (författare)
Feyziyev, YasharLund 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(Swepub:lu)biok-yfe (författare)
Styring, StenbjörnLund 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(Swepub:lu)biok-sst (författare)
Biokemi och StrukturbiologiCentrum för Molekylär Proteinvetenskap (creator_code:org_t)

Sammanhörande titlar

Ingår i:Biochemistry: American Chemical Society (ACS)41:18, s. 5830-58430006-29601520-4995

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Av författaren/redakt...: Bernat, Gabor; Morvaridi, Susan ...; Feyziyev, Yashar; Styring, Stenbjö ...

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NATURVETENSKAP: NATURVETENSKAP; och Biologi; och Biokemi och mole ...

Artiklar i publikationen: Biochemistry

Av lärosätet: Lunds universitet

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