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Volume 42, Nº 1 (2025)
Articles
Oxygenic photosynthesis: induction of chlorophyll a fluorescence and regulation of electron transport in thylakoid membranes in silico
Resumo
The paper describes an extended mathematical model for the regulation of the key stages of electron transfer in the photosynthetic chain of electron transport (CET) and the associated processes of trans-thylakoid proton transfer and ATP synthesis in chloroplasts. This model includes primary plastoquinone PQA, associated with photosystem 2 (PS2), and secondary plastoquinone PQB, exchanging with plastoquinone molecules that are part of the pool of electronic carriers between PS2 and photosystem 1 (PS1). The model adequately describes the multiphase non-monotonic curves of chlorophyll fluorescence induction and the kinetics of P700 redox transformations (photoreaction center PS1), plastoquinone, changes in ATP and pH concentrations in lumen (pHin) and stroma (pHout) depending on the illuminating conditions of chloroplasts (variation in intensity and spectral composition of light). The results of computer simulation are consistent with experimental data on the kinetics of photoinduced P700 transformations in the leaves of higher plants and the induction of chlorophyll a fluorescence. The obtained data are discussed in the context of "short-term" mechanisms of pH-dependent regulation of electron transport in intact chloroplasts (non-photochemical quenching of excitation in PS2 and activation of Calvin–Benson cycle reactions).
3-19
Interaction of albumin with angiotensin-I-converting enzyme according to molecular modeling data
Resumo
Human serum albumin (HSA) is an endogenous inhibitor of angiotensin-I-converting enzyme (ACE), an integral membrane protein that catalyzes the cleavage of angiotensin I decapeptide to angiotensin II octapeptide. By inhibiting ACE, HSA plays a key role in the renin-angiotensin-aldosterone system (RAAS). However, little is known about the mechanism of interaction between these proteins; the structure of the HSA–ACE complex has not yet been obtained experimentally. The purpose of the present work is to investigate the interaction of HSA with ACE in silico. Ten possible HSA–ACE complexes were obtained by the procedure of macromolecular docking. Based on the number of steric and polar contacts between the proteins, the leading complex was selected, the stability of which was then tested by molecular dynamics (MD) simulation. An analysis of the possible effect of modifications in the albumin molecule on its interaction with ACE was performed. A comparative analysis of the structure of the HSA–ACE complex obtained by us, was performed with the known crystal structure of the HSA complex with neonatal Fc receptor (FcRn). The molecular modeling data outline the direction for further study of the mechanisms of HSA–ACE interaction in vitro. Information about these mechanisms will help in the design and improvement of pharmacotherapy aimed at modulating the physiological activity of ACE.
20-30
Simulation of the glycolytic metabolites concentration profile in mammalian resting skeletal muscles
Resumo
For the first time, a mathematical model of glycolysis in mammalian skeletal muscles is presented, in which stationary concentrations of glycolysis metabolites are in good agreement with experimental data obtained in resting muscles. The correspondence between the model and experimental values of metabolite concentrations was achieved due to enhancing the inhibitory effect of ATP on pyruvate kinase and significantly reducing the ratio of [NAD]/[NADH] concentrations in the cytoplasm of skeletal muscles. At the same time, in order for glycolysis to provide the rate of ATP production necessary for activation of muscle load, an activation of muscle pyruvate kinase by fructose-1,6-diphosphate was included in the model.
31-44
Electrostatic potentials during adsorption and photochemical reactions of pyranine on bilayer lipid membranes
Resumo
Adsorption and photochemical reactions of pyranine on a bilayer lipid membrane (BLM) have been studied by measuring electrostatic potentials at the membrane–water interface. The dependence of the electrostatic potentials due to the adsorption of pyranine on its concentration in solution is described by the Gouy–Chapman theory assuming that anions with three charged groups are adsorbed on the membrane. No significant changes in the boundary potential were found when BLM with pyranine adsorbed on it was illuminated. Significant changes in the potential were observed if molecules of styryl dyes di-4-ANEPPS or RH-421 were adsorbed on BLM in addition to pyranine. The sign and magnitude of these changes correspond to the disappearance of the dipole potential created by styryl dye molecules on the BLM. The rate of potential disappearance was proportional to pyranine concentration and illumination intensity. The disappearance of the potential can be caused either by the binding of protons released from the pyranine molecule to the dye molecules with their subsequent desorption from the BLM or by their destruction. Pyranine and styryl dye molecules can form complexes at the BLM boundary. This is evidenced by experiments in which the sum of the potential changes caused by their adsorption separately differed significantly from the change in the boundary potential during their simultaneous adsorption. The kinetics of the disappearance of the dipole potential of BLM with styryl dyes upon excitation of pyranine turned out to be similar to that observed earlier with another compound, 2-methoxy-5-nitrophenyl sodium sulfate, which releases protons at the membrane boundary upon illumination (Konstantinova et al., 2021. Biochem. (Mosc.), Suppl. Series A: Membr. Cell Biol. 15 (2), 142–146). This suggests that it is associated with the desorption of dye molecules from the membrane, due to the binding of protons released from excited pyranin molecules to them.
45-52
Approach for analysis of intracellular markers in phosphatidylserine-positive platelets
Resumo
Phosphatidylserine (PS)-positive platelets play an important role in thrombosis and hemostasis. They have high procoagulant activity, the ability to vesiculate, and can aggregate with activated PS-negative platelets. They are found in growing thrombus in vitro, but there remain a number of mysteries associated with them. In particular, intracellular signaling and cytoskeletal reorganization in these platelets is very poorly studied, because they are destroyed upon permeabilization, which is necessary for antibodies to intracellular markers to penetrate the cell. In this work, we propose an approach that allows the analysis of intracellular signaling in calcium ionophore A23187-induced PS-positive platelets using flow cytometry or confocal microscopy. We used the mildest permeabilization of fixed PS-positive platelets using saponin and showed that such permeabilization allows us to preserve PS-positive platelets. As an example, we analyzed the state of the polymerized form of actin in PS-positive platelets and showed that, despite the significant rearrangement of the cytoskeleton that occurs upon activation in such platelets, actin in them is partially presented in a polymerized form.
53-60
Comparison of spontaneous and evoked activity of CA1 pyramidal cells and dentate gyrus granule cells of the hippocampus at an increased extracellular potassium concentration
Resumo
We studied the effect of changing extracellular potassium concentration ([K+]o) on spontaneous and evoked burst activity of glutamatergic neurons in the mouse hippocampus using whole-cell patch clamp. We show that increasing [K+]o from 3 to 8.5 mM (potassium load) induced spontaneous tonic (1) and pacemaker burst (2) activity of CA1 pyramidal cells (20% and 10% of the total number of cells, respectively). In contrast to CA1, potassium loading did not lead to the appearance of pacemaker granule cells in the dentate gyrus (DG). Similarly, potassium load increased the evoked burst activity of CA1 pyramidal cells and, paradoxically, suppressed the burst activity of DG granule cells over the entire range of current steps from 10 to 200 pA. Potassium load shifted the current-voltage characteristics to the right and substantially increased inward currents in CA1 and DG cells. Inward and outward currents of DG neurons were 4–4.5 times as high as those of CA1 cells. The possible involvement of potassium-activated potassium-conducting channels is discussed in the bimodal effect of potassium load on the excitability of CA1 and DG glutamatergic neurons. Our results suggest that CA1 pyramidal cells may be more sensitive to potassium load than DG granule cells, which may play a role in hyperexcitation of neural networks during epileptogenesis.
61-70
Membrane-protective properties of lipid extract from marine brown alga Sargassum pallidum (Turner) C. Agardh under experimental stress conditions
Resumo
The effect of lipid extract isolated from the thallus of the marine brown alga Sargassum pallidum and a commercial reference preparation "Omega-3" on biochemical parameters of rat erythrocyte membranes under experimental stress was studied. Stress exposure (vertical fixation by the dorsal neck fold for 24 h) was accompanied by an increase in erythrocyte diameter and average volume, as well as a decrease in osmotic resistance to changes of NaCl concentration. The erythrocyte membrane exhibited an increase in cholesterol levels and alterations in the quantitative characteristics of phospholipid classes and their constituent fatty acids, which resulted in the appearance of modified molecular fractions of phospholipids. The correction of these changes was achieved through the administration of the lipid extract of S. pallidum and the reference preparation "Omega-3". The S. pallidum extract demonstrated comparable biological efficiency to the reference preparation "Omega-3", yet exhibited superior efficacy in restoring the dimensional characteristics of erythrocytes, as well as the ratio of phospholipid fractions in erythrocyte membranes and the values of their fatty acid composition. The pharmacological effect of the S. pallidum lipid extract is believed to be due to a wider range of neutral and phospholipid classes, as well as polyunsaturated fatty acids of n-3 and n-6 families, which provide effective repair of erythrocyte membranes. We believe that S. pallidum thallus can be used as a raw material for the preparations with stress-protective and lipid-correcting properties.
71-84