Том 64, № 3 (2019)

Abstract—A theoretical assessment of the half-width of the conformational transition of macromolecules caused by an increase in pressure is presented. It is shown that the half-width is determined mainly by the change (jump) of the volume during the transition. A formula similar to van-Goff’s formula for the half-width of transitions caused by temperature increase is obtained, which makes it possible to estimate the effective change in volume for a one-stage transition under the influence of pressure by its half-width. The estimates show that the “gel–liquid crystal” transitions in phospholipids have a half-width of several megapascals (tens of atmospheres), while in proteins it is approximately 100 times higher and equals hundreds of megapascals (several thousand atmospheres). It is shown that the volume jump can significantly change in the interval from the beginning to the end of the transition during denaturation of proteins under the influence of pressure.

Abstract—Variants of miniplasminogen with an altered primary structure have been designed to study previously described changes in tryptophan fluorescence during plasminogen activation by urokinase. Miniplasminogens that contain the Trp141, Trp215, and Leu217 substitutions (the position of the amino-acid residue is specified by the Chymotrypsin nomenclature) have been tested. The activation of mutants containing a single tryptophan substitution induced changes in the fluorescence spectrum. No changes in the fluorescence spectrum were observed in the case of miniplasminogen containing a double tryptophan substitution. This indicates that both Trp141 and 215 contribute to the fluorescence spectrum shift; however, as suggested previously, the contribution of changes in the Trp215 microenvironment is greater. The Trp141, Trp215, and Leu217 amino-acid substitutions in miniplasminogen have no effect on the rate of plasminogen activation by urokinase. The replacement of the conserved Trp215 residue in serine proteases led to a significant reduction but not loss of the amidolytic activity of plasmin.

Abstract—Changes in the level of DNA damage induced by atmospheric factors were evaluated from the percentage of tail DNA (%TDNA) in the comet assay of mouse cells for blood leukocytes, Ehrlich ascites carcinoma, and P388 lymphocytic leukemia. It was shown that (1) the values of DNA damage of blood leukocytes (%TDNA) were high within narrow ranges of atmospheric temperature (from –4°С to +3°С) and atmospheric partial oxygen contents within 298–304 mg/L; (2) the range of variations in %TDNA of leukocytes increased with increasing geomagnetic activity; (3) the changes in %TDNA of intact and X-irradiated (4 Gy) leukocytes and of tumor cells were associated with changes in air temperature; and (4) %TDNA correlated with atmospheric temperature in both types of intact tumor cells and irradiated P388 cells. Thus, variations in %TDNA appear to be caused by reactive oxygen species generated in the environment at temperatures of phase transitions of water. It is conceivable that changes in the basal %TDNA of cells modulate their radiation response.

Abstract—The paper presents the results of monitoring of the photosynthetic activity of the green microalga Chlorella. A thermophilic strain of Chlorella with a high rate of cell division was cultivated in a photobioreactor. Three medium variants with different mineral composition were used. Chlorophyll fluorescence induction curves and microalgal suspension absorption spectra were recorded every hour during 40-hour culture growth for each medium. The method of spectral multiexponential approximation we have developed was used to analyze 120 induction curves obtained after monitoring. This method revealed the dynamics of gradual changes in the number of phases of induction curves, their amplitudes and characteristic times during culture growth. The relationship between the parameters of induction curves and electron transfer processes in the reaction center of photosystem II allowed for interpretation of the changes in the shape of the induction curves in terms of the processes in the reaction center of photosystem II. The spectral multiexponential approximation method was shown to be highly sensitive to physiological state of microalgae and suitable for analyzing a huge amount of experimental data. The physiological processes accompanying the depletion of nitrogen in the environment are discussed.

Abstract—Red blood cells of rats were exposed to the earth’s magnetic field and an attenuated magnetic field in the presence of tert-butyl hydroperoxide to induce oxidative stress. Spectral analysis within the wavelength range of 500–700 nm was used to estimate the concentration of three forms of hemoglobin: oxyhemoglobin, methemoglobin, and hemichrome, released during erythrocyte hemolysis. The concentration of reactive oxygen species was determined in samples by spin trapping using electron paramagnetic resonance. It was found that after 4 h of incubation at high tert-butyl hydroperoxide concentrations (>700 μM), red blood cells that were exposed to an attenuated magnetic field released considerably more (p < 0.05) hemoglobin, mostly methemoglobin. After 24 h of incubation at low tert-butyl hydroperoxide concentrations (≤350 μM), erythrocytes that were exposed to the earth’s magnetic field released relatively more (p < 0.001) hemoglobin, with methemoglobin as a major form of total hemoglobin. Red blood cells exposed to the attenuated magnetic field generated more oxygen radicals than cells exposed to the earth’s magnetic field. Under certain oxidative stress conditions, the attenuated magnetic field can impair the functional state of red blood cells and provoke cell death. However, low concentrations of reactive oxygen species can neutralize attenuated magnetic field effects.

Abstract—The ketogenic diet is used as a treatment for different brain diseases. It involves replacement of dietary carbohydrates with fat, which leads to production of ketone bodies, predominantly β-hydroxybutyrate. The mechanism of the protective effect of the ketogenic diet remains poorly studied. In this work, the combined influence of glucose and β-hydroxybutyrate on the potentials of the synaptosomal plasma membrane and the mitochondrial membrane was investigated. It was found that the presence of ketone bodies in a glucose-containing incubation medium did not affect the synaptosomal plasma membrane potential, in contrast to what was previously observed for the neuronal plasma membrane. It was shown that incubation of synaptosomes in the medium containing only β-hydroxybutyrate resulted in mitochondrial depolarization (ΔΨ change). At the same time, the presence of ketone bodies in the glucose-containing incubation medium led to mitochondrial hyperpolarization. The observed depolarization was partially compensated by an increase in mitochondrial ΔpH, which was induced by mitochondrial depolarization as such, but not by the presence of β-hydroxybutyrate. Thus, ketone bodies can be utilized by synapses as energy substrates, but β-hydroxybutyrate is a less effective energy source than glucose.

Abstract—Statistics were obtained for background firing activity recorded from several neurons of the auditory center of the midbrain (semicircular torus) in the common frog. The methods were those used to analyze the temporal flow of fractal point processes. Most neurons showed a power-law increase in the variance-to-mean ratio (Fano factor) of pulse number with the time window increasing from hundreds of milliseconds to several tens of seconds, although cells whose background firing activity was close to random were also observed. A method based on the registration of local features (the Allan factor as a function of the same time window) confirmed the fractal properties for many cells. A power-law growth of the Allan factor usually began at large time windows. The third method of fractal analysis (the Hurst index) also argued in favor of the randomness and fractality of background firing activity. The relationships with other statistics of random point processes were analyzed for the fractal characteristics. A comparison with data obtained for neurons of the medulla oblongata indicated that the variability of firing activity slight increases along the auditory pathway.

Abstract—The effect of pulsed terahertz radiation at a wavelength of 66 μm, a pulse duration of 100 ns, and a pulse energy of 200 mJ on a suspension of microbial cells was studied. The effect of terahertz radiation was shown to cause cell death at a value of total energy of ~6 J. Since the temperature of the cell suspension after radiation remained almost unchanged, it implies that pulsed terahertz radiation exhibited a non-thermal effect. Methods of standard microbial plating, electron microscopy, electroacoustic analysis, and spectral analysis were used in order to verify the results. These experiments make it possible to control the viability of bacterial cells using terahertz radiation with certain parameters.

Abstract—Tumor cells have a higher basal ROS level than normal cells. This phenomenon may provide grounds for the development of novel antitumor drugs that are capable of selectively inducing oxidative stress in tumor cells. This approach can involve agents that induce ROS production and/or inhibit cellular enzymatic antioxidant systems. Thioredoxin reductase is a key enzyme in such systems. Overexpression of thioredoxin reductase has been shown in several types of tumors of hematopoietic, lymphoid, and other tissues. The results of studies of the antitumor activities of various synthetic and natural substances that are able to inhibit thioredoxin reductase are summarized. It is shown that thioredoxin reductase inhibition results in an increase in ROS level in tumor cells and oxidative damage of cells followed by apoptosis mainly via the mitochondrial pathway.

Abstract—In this work, the electrical activity of the heterogeneous intact sinoatrial node at interaction with the atrial myocardium is simulated based on a detailed approach. The reduction of this model used the methods of the theory of similarity. The results of the calculation of the reduced model are compared with the solutions obtained in the initial model. The model also found that an increase in the number of non-excitable sites in the atrial myocardium bordering the pacemaker causes a slowdown in the overall rhythm of electrical activity.

Abstract—The goal of the present study was to evaluate the mechanism of the systemic response to helium-generated cold plasma based on heart rate variability indices in rats. The experiments were performed using 20 male Wistar rats. The animals were divided into two equal groups containing 10 rats per each group. In animals of the control group, a single measurement of the microcirculation indices was performed. The rats of the experimental group were exposed to helium-generated cold plasma applied onto the skin on the back (1 min) for 10 days. Helium-generated cold plasma was produced with a special device designed at the Institute of Applied Physics (Nizhny Novgorod, Russia) using the principle of microwave-induced ionization of the gas stream. The electrocardiograms were recorded using a Polyspectr diagnostic complex (Ivanovo, Russia). The statistical analysis of the electrocardiograms and calculation of spectral parameters was performed according to the standard algorithms. It has been found that the exposure to helium-generated cold plasma led to the formation of non-specific (adaptive) changes in heart rate. These changes manifested in the form of moderate tachycardia, the activation of sympathetic stimulation of myocardium, and a proportional decrease in the spectrum power within all frequency ranges.

Abstract—This article discusses the relevant results on early and safe detection of breast cancer with a thermal volume tomography (TVT) device produced in Russia. The device records and analyzes the spatial temperature distribution on the skin in the tumor region. The resulting dataset can be analyzed using artificial intelligence methods, which make it possible to efficiently choose the treatment strategy by selecting optimal treatments at the preclinical stage of breast cancer.