Is carbonic anhydrase activity of photosystem II required for its maximum electron transport rate?
It is known, that the multi-subunit complex of photosystem II (PSII) and some of its single proteins exhibit carbonic anhydrase activity. Previously, we have shown that PSII depletion of HCO3-/CO2 as well as the suppression of carbonic anhydrase activity of PSII by a known inhibitor of α‑carbonic anhydrases, acetazolamide (AZM), was accompanied by a decrease of electron transport rate on the PSII donor side. It was concluded that carbonic anhydrase activity was required for maximum photosynthetic activity of PSII but it was not excluded that AZM may have two independent mechanisms of action on PSII: specific and nonspecific. To investigate directly the specific influence of carbonic anhydrase inhibition on the photosynthetic activity in PSII we used another known inhibitor of α‑carbonic anhydrase, trifluoromethanesulfonamide (TFMSA), which molecular structure and physicochemical properties are quite different from those of AZM. In this work, we show for the first time that TFMSA inhibits PSII carbonic anhydrase activity and decreases rates of both the photo-induced changes of chlorophyll fluorescence yield and the photosynthetic oxygen evolution. The inhibitory effect of TFMSA on PSII photosynthetic activity was revealed only in the medium depleted of HCO3-/CO2. Addition of exogenous HCO3- or PSII electron donors led to disappearance of the TFMSA inhibitory effect on the electron transport in PSII, indicating that TFMSA inhibition site was located on the PSII donor side. These results show the specificity of TFMSA action on carbonic anhydrase and photosynthetic activities of PSII. In this work, we discuss the necessity of carbonic anhydrase activity for the maximum effectiveness of electron transport on the donor side of PSII.
['Shitov|Alexandr V|AV|', 'Terentyev|Vasily V|VV|', 'Zharmukhamedov|Sergey K|SK|', 'Rodionova|Margarita V|MV|', 'Karacan|Mehmet|M|', 'Karacan|Nurcan|N|', 'Klimov|Vyacheslav V|VV|', 'Allakhverdiev|Suleyman I|SI|']
D000086:Acetazolamide D001639:Bicarbonates D002245:Carbon Dioxide D002257:Carbonic Anhydrase Inhibitors D002256:Carbonic Anhydrases D002734:Chlorophyll D000077194:Chlorophyll A D004579:Electron Transport D004583:Electrons D006863:Hydrogen-Ion Concentration D007700:Kinetics D008027:Light D008698:Mesylates D010100:Oxygen D018532:Peas D010788:Photosynthesis D045332:Photosystem II Protein Complex D020524:Thylakoids
Carbonic anhydrase Photosystem II Inhibitor Sulfonamide