Is carbonic anhydrase activity of photosystem II required for its maximum electron transport rate?

Abstract

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 HCO/CO 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 HCO/CO. Addition of exogenous HCO 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.

The Main Structural and Functional Characteristics of Photosystem-II-Enriched Membranes Isolated from Wild Type and cia3 Mutant Chlamydomonas reinhardtii

“…The rate of photosynthetic oxygen evolution was measured at 25 • C with a Clarke-type electrode, in a 1-mL cell (Hansatech Instruments Ltd., Norfolk, UK) as it was performed previously [22,40,43] at 1950 µmol photons m −2 s −1 of red light (λ > 600 nm). Measurements were carried out in medium, containing either 20 mM MES-NaOH (pH 6.5) or 20 mM MOPS-NaOH (pH 7.0) and 35 mM NaCl, 400 mM sucrose.…”

Sulfonamides influence on the activity of thylakoid ATPase isolated from spinach chloroplasts

“…The inhibitory effect of sulfonamides on the activity of carbonic anhydrase depends on their solubility in water, pKa, and pH of the medium, since these inhibitors are active only in ionized form [24]. Therefore, the proportion of ionized molecular forms with pKa < 6.0 at physiological pH values significantly exceeds the relative amount of ionized inhibitors with pKa > 8.…”

Вплив Водорозчинних Сульфаніламідів На Активність Тилакоїдної Атф-Ази, Ізольованої З Хлоропластів Шпинату

“…Вона, зокрема, здатна вибірково пригнічувати гідроліз АТФ. Кілька експериментальних досліджень показують, що ця регуляція досягається завдяки великим конформаційним змін α-спірального C-кінцевого домену ε-субодиниці [23]. Дані свідчать, що обидва препарати пригнічували швидкість гідролізу АТФ, але в різному ступені.…”