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. 2008 Jan 31;27(5):782–791. doi: 10.1038/emboj.2008.12

Figure 4.

Figure 4

Bicarbonate stimulates O2 evolution in PSII(Cah3−) by facilitating proton transfer away from WOC. (A) Stimulatory effect of the amphiphilic pH indicator NR on the O2 evolution rate of membrane fragments from cia3. PSII(Cah3−), 1; PSII(Cah3−) in the presence of 20 μM NR, 2; in the presence of 40 μM NR, 3 and in the presence of 40 μM NR and 2 mM KHCO3, 4. The initial rate of O2 evolution (indicated as 100% level in the figure) was 183 μmol O2 (mg Chl)−1 h−1. The assay medium was depleted of endogenous Ci and the Chl concentration was 15 μg ml−1. All measurements were conducted at 25°C in the presence of 1 mM DCBQ and 0.5 mM FeCN. Values are means±s.e. (n=4). (B) Rate of O2 evolution in PSII membrane fragments from the cia3 mutant measured in H2O and D2O media. PSII(Cah3−) in SMS buffer, 1; PSII(Cah3−) in SMS buffer in the presence of 1 mM KHCO3, 2; PSII(Cah3−) in D2O-SMS buffer, 3 and PSII(Cah3−) in D2O–SMS buffer in the presence of 1 mM KHCO3, 4. The kH2O/kD2O in the PSII(Cah3−) was 1.78 and 1.15 in wt PSII. Values are means±s.e. (n=6). The initial rate of O2 evolution (indicated as 100% level) was 190 μmol O2 (mg Chl)−1 h−1.