Effects of Novel Photosynthetic Inhibitor [CuL2]Br2 Complex on Photosystem II Activity in Spinach

Sergey K Zharmukhamedov; Mehriban S Shabanova; Margarita V Rodionova; Irada M Huseynova; Mehmet Sayım Karacan; Nurcan Karacan; Kübra Begüm Aşık; Vladimir D Kreslavski; Saleh Alwasel; Suleyman I Allakhverdiev

doi:10.3390/cells11172680

Effects of Novel Photosynthetic Inhibitor [CuL₂]Br₂ Complex on Photosystem II Activity in Spinach

Cells. 2022 Aug 28;11(17):2680. doi: 10.3390/cells11172680.

Affiliations

¹ Institute of Basic Biological Problems, FRC PSCBR RAS, 142290 Pushchino, Russia.
² Bionanotechnology Laboratory, Institute of Molecular Biology and Biotechnology, Azerbaijan National Academy of Sciences, AZ1073 Baku, Azerbaijan.
³ K.A. Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya Street 35, 127276 Moscow, Russia.
⁴ Department of Chemistry, Science Faculty, Gazi University, Teknikokullar, Ankara 06500, Turkey.
⁵ College of Science, King Saud University, Riyadh 12372, Saudi Arabia.
⁶ Department of Plant Physiology, Faculty of Biology, M.V. Lomonosov Moscow State University, Leninskie Gory 1-12, 119991 Moscow, Russia.

Abstract

The effects of the novel [CuL₂]Br₂ complex (L = bis{4H-1,3,5-triazino [2,1-b]benzothiazole-2-amine,4-(2-imidazole)}copper(II) bromide complex) on the photosystem II (PSII) activity of PSII membranes isolated from spinach were studied. The absence of photosynthetic oxygen evolution by PSII membranes without artificial electron acceptors, but in the presence of [CuL₂]Br₂, has shown that it is not able to act as a PSII electron acceptor. In the presence of artificial electron acceptors, [CuL₂]Br₂ inhibits photosynthetic oxygen evolution. [CuL₂]Br₂ also suppresses the photoinduced changes of the PSII chlorophyll fluorescence yield (F_V) related to the photoreduction of the primary quinone electron acceptor, Q_A. The inhibition of both characteristic PSII reactions depends on [CuL₂]Br₂ concentration. At all studied concentrations of [CuL₂]Br₂, the decrease in the F_M level occurs exclusively due to a decrease in Fv. [CuL₂]Br₂ causes neither changes in the F₀ level nor the retardation of the photoinduced rise in F_M, which characterizes the efficiency of the electron supply from the donor-side components to Q_A through the PSII reaction center (RC). Artificial electron donors (sodium ascorbate, DPC, Mn²⁺) do not cancel the inhibitory effect of [CuL₂]Br₂. The dependences of the inhibitory efficiency of the studied reactions of PSII on [CuL₂]Br₂ complex concentration practically coincide. The inhibition constant Ki is about 16 µM, and logKi is 4.8. As [CuL₂]Br₂ does not change the aromatic amino acids' intrinsic fluorescence of the PSII protein components, it can be proposed that [CuL₂]Br₂ has no significant effect on the native state of PSII proteins. The results obtained in the present study are compared to the literature data concerning the inhibitory effects of PSII Cu(II) aqua ions and Cu(II)-organic complexes.

Keywords: aromatic amino acids intrinsic fluorescence; copper; metalorganic complexes; oxygen evolution; photosynthetic inhibitors; photosystem II.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Chlorophyll / metabolism
Electron Transport
Oxygen / metabolism
Photosystem II Protein Complex* / metabolism
Spinacia oleracea* / metabolism

Substances

Photosystem II Protein Complex
Chlorophyll
Oxygen

Grants and funding

This work was funded by the Russian Science Foundation (19-14-00118) to S.K.Z., V.D.K. and S.I.A., M.S.S. were supported by grant from AzSF (EİF-GAT-6-2021-2(39)-13/06/3-M-06). Figure 7 was obtained under the state contract of the Ministry of Science and Higher Education of the Russian Federation (Project No. 122050400128-1). S.A. would like to thank the Distinguished Scientists Fellowship Program, King Saud University, Saudi Arabia, for their support.