Vol 42, No 3 (2025)

In this work, we carried out mathematical modeling of the electron and proton transport regulation in the thylakoid membranes of chloroplasts under different operating conditions of the electron transport chain (ETC) of chloroplasts. The study is based on the kinetic model of the functioning of the chloroplasts ETC proposed by us earlier, which describes the redox transformations of the reaction center of photosystem 1 (PS1), ferredoxin molecules, several forms of plastoquinone (PS2-related molecules PQ_A, PQ_B, and the pool of plastoquinones PQ/PQH₂), as well as plastocyanin molecules. The model also simulates the induction curve of chlorophyll a fluorescence in the leaves of higher plants adapted to darkness. The multiphase kinetic curves obtained by varying the model parameters reflecting the rate of functioning of the Calvin–Benson cycle and the cyclic electron transport path around PS1 are in reasonable agreement with the published experimental data. The main result of our work is that it mathematically describes how pH-dependent regulatory processes occurring in various parts of the chloroplast ETC (non-cyclic, cyclic, and pseudocyclic electron transport) affect the kinetics of induction processes (slow induction of fluorescence and redox transformations of the PS1 photoreaction center) in dark-adapted chloroplasts of plants.

This study demonstrates the effect of the rhodocyanine derivative MKT-077 on the function of isolated mitochondria from mouse skeletal muscle. MKT-077 was shown to dose-dependently inhibit mitochondrial respiration fueled by glutamate/malate (complex I substrates) or succinate (complex II substrate). This effect of MKT-077 was accompanied by a decrease in the membrane potential of organelles and was associated with both inhibition of the activity of complexes I and II of the mitochondrial respiratory chain and an increase in the proton permeability of the inner mitochondrial membrane. Molecular docking revealed sites in mitochondrial respiratory chain complex I that have an affinity for MKT-077 comparable to that of the specific inhibitor rotenone. At a concentration of 5 μM, MKT-077 caused a significant increase in hydrogen peroxide production by skeletal muscle mitochondria. However, 1 μM MKT-077 reduced the pro-oxidant effect of antimycin A. In addition, MKT-077 dose-dependently reduced the ability of mitochondria to uptake and retain calcium ions in the matrix. The article discusses the mechanisms of possible action of MKT-077 on the functioning of skeletal muscle mitochondria and their contribution to the side effects observed during the therapy of pathological conditions in vivo using this rhodocyanine derivative.

The effect of 100 μM cadmium ions (Cd²⁺) on the content of ∆5-sterols in microdomains of the vacuolar membrane was studied. Cd²⁺ was shown to cause an increase in the content of sterols in the tonoplast microdomains of zone 2 of the sucrose gradient and a decrease in the sterol content in zone 4. The sum of free sterols was higher than the sum of sterol esters in both the tonoplast and microdomains of zones 2, 4, and 6. The composition of free sterols in microdomains was dominated by β-sitosterol, and in the tonoplast by stigmasterol. The composition of sterol esters in the tonoplast also showed a high content of stigmasterol and a high content of β-sitosterol and campesterol in zone 2 microdomains. Compared with controls not exposed to Cd²⁺, changes in the % content of ∆5-sterols were observed. The changes affected mainly sterols involved in the structural organization of the lipid bilayer. These results suggest that sterols of tonoplast microdomains may participate in the cell response to Cd²⁺.

The existence of fat taste along with the generally recognized taste modalities (sweet, bitter, umami, salty, and sour) is currently a subject of scientific debate and active research. Available data on the signaling cascade triggered by long-chain fatty acids (FAs) in the taste cell indicate its similarity to the transduction of sweet, bitter, and umami stimuli, but the initial stages of transduction of fatty stimuli remain unclear. A member of the G-protein-coupled receptor superfamily, GPR120, is considered as one of the candidates for the role of a long-chain FA receptor operating in the taste bud. At the same time, available reports implicating GPR120 in the FA perception by the peripheral taste system are highly contradictory. In order to create a platform for further study of the contribution of GPR120 to FA transduction, we cloned GPR120 from the mouse taste tissue and expressed it in HEK-293 cells. In contrast to the parental HEK-293 cells, GPR120-positive HEK-293 cells generated receptor-like Ca²⁺ transients in response to long-chain FA application, thus confirming the literature data on the coupling of the GPR120 receptor to the phosphoinositide cascade and intracellular Ca²⁺ mobilization. The HEK-293 cells expressing recombinant GPR120 receptor may present a useful cell model for screening natural and synthetic ligands of this receptor and analyzing its coupling to intracellular signaling pathways. Co-expression of GPR120 with other signaling proteins involved in the transduction of fatty stimuli in taste cells may be useful for interpreting taste cell responses to FAs.