Том 61, № 3 (2016)

The circular dichroism spectra of liquid-crystalline dispersions obtained by phase exclusion of linear double-stranded DNA molecules from aqueous saline solutions of polyethylene glycol (120 ≤ C_PEG ≤ 300 mg/mL) have been investigated. The formation of liquid-crystalline dispersions at polyethylene glycol concentrations ranging from 120 to 200 mg/mL was accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism; this is indicative of cholesteric packing of the double stranded DNA molecules in the particles of the dispersion. Liquid-crystalline dispersions formed at PEG concentrations higher than 220 mg/mL and room temperature did not show any abnormal bands in the circular dichroism spectra; this is indicative of hexagonal packing of double-stranded DNA molecules in the particles of the dispersions. Heating of optically inactive liquid crystal dispersions induced a transition of the dispersions into a different state accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism. This transition is considered within the concept of the transformation of a hexagonal packing of DNA molecules into a cholesteric packing. A qualitative mechanism of such a transition is proposed that is formulated in the terms of the “quasinematic” layers of double-stranded DNA molecules that change their spatial orientation under the competing influences of the osmotic pressure of the solvent, orientational elasticity of the cholesteric packing, and thermal fluctuations.

A quantitative evaluation of the accuracy of the rapid-equilibrium assumption in steady-state enzyme kinetics was obtained for a multipath arbitrary enzyme mechanism with a number of equilibrium segments. Explicit expressions for estimating the contribution of any equilibrium segment to the accuracy of the rapid-equilibrium assumption were obtained. This allowed us to determine the accuracy of the rapid-equilibrium assumption (Δ) in general: 1 + Δ = (1 + Δ₁)(1 + Δ₂)... (1 + Δ_k), where Δ₁, Δ₂,..., Δ_k is the contribution of each individual equilibrium segment. The accuracy depends only on the structure and properties of equilibrium segments, which have been accounted for in the rapid-equilibrium assumption, but it is independent of the number of paths in the mechanism of the enzymatic reaction and on the structure and properties of the remaining part (steady-state) of the kinetic scheme.

Processes that occur in the ensemble of photosynthetic electron transport systems have been modeled using a kinetic Monte Carlo method. The size of a simulated ensemble (3–5 million elementary photosynthetic chains) corresponds to the number of photosynthetic reaction centers in a plant cell. The method enables one to modify the structure of a model system according to different concepts of the organization of processes in a photosynthetic membrane. Using this model, the experimental kinetics of the chlorophyll fluorescence induction associated with the Photosystem II and the redox transformations of a photoactive pigment of the Photosystem I have been successfully reproduced. The model was verified by comparing the calculated fluorescence induction curves to experimental curves, obtained in the presence of various photosynthesis inhibitors and under temperature inactivation of the Photosystem II donor side.

The erythrocyte intracellular pressure was calculated using a biomechanical model of the erythrocyte and atomic-force-microscopy (AFM) data. The intracellular pressure was characterized as a function of the model erythrocyte morphology. Based on numerical modeling and data of erythrocyte imaging by AFM, a method was developed to estimate the erythrocyte intracellular pressure by comparing experimental data and the results of numerical calculations. Calculations were performed for erythrocytes of dwarf domestic pigs with and without obstructive jaundice that varied in severity. The erythrocyte membrane was affected with increasing disease severity and blood bilirubin concentration, i.e., the erythrocyte volume increased on average, and substantial changes were observed for erythrocyte intracellular pressure relative to its normal value. As an example, an increase in bilirubin concentration from 5 to 96 μmol/L was associated with an increase in intracellular pressure from 0 to 2.2 kPa. An examination of the erythrocyte membrane surface by high-resolution AMF showed that the membrane is disrupted with an increase in bilirubin concentration and displays lesions and an increasing rupture length.

Hypochlorous acid-modified human blood low density lipoprotein (LDL–HOCl) was shown to stimulate neutrophils and to increase the luminol- (lm-CL) or lucigenin-enhanced chemiluminescence (lc-CL) of neutrophils. Antioxidants and HOCl scavengers (glutathione, taurine, cysteine, methionine, ceruloplasmin, and human serum albumin (HSA)) were tested for effects on lm-CL, lc-CL, H₂O₂ production, and degranulation of azurophilic granules of neutrophils. All agents used in increasing concentrations were found to decrease lm-CL produced by neutrophils upon stimulation with LDL–HOCl or subsequent treatment with the activator phorbol 12-myristate 13-acetate (PMA). The agents exerted a far lower, if any, effect on lc-CL and the H₂O₂ production by neutrophils in the same conditions. In the majority of cases, a decline in neutrophil chemiluminescence in the presence of the agents was not related to their effect on neutrophil degranulation, but was most likely due to their direct interactions with reactive halogen (RHS) or oxygen (ROS) species generated upon neutrophil activation or to myeloperoxidase (MPO) inhibition. Antioxidants and HOCl scavengers present in the human body were assumed to decelerate the development of oxidative or halogenative stress and thereby prevent neutrophil activation.

The effect of an extremely weak static magnetic field (EWSMF) was studied in diploid fibroblast strains that originated from a healthy donor and an ataxia–telangiectasia patient. Indirect immunofluorescence was used to detect p53, p53BP1, and p21. The pattern that occurred in donor cells exposed to EWSMF similar to that observed in DNA damage, viz., the p53 and p21 levels increased and p3BP1 foci formed. No visible change was observed in primary fibroblasts from the ataxia–telangiectasia patient. The results implicate ATM signaling in the fibroblast response to EWSMF.

This paper updates our knowledge on quantitative laser scanning microscopy and summarizes the capabilities of this method as applied to cytometry and analysis of cell structure of the mouse early embryo and the oocyte. This method requires a stack of optical sections obtained as Z-series with subsequent 3D reconstruction. This approach was used for visualization of the 3D cell model, measurement of the cell volume and surface area, as well as a study of the cell interior via optical sections. To maintain the dimensional characteristics of embryos or oocytes the method of sample preparation involved the following consequent steps: rapid cryofixation, low-temperature dehydration, infiltration by optically transparent mounting media, and laser-scanning microscopy. This strategy enables volume measurement, even in the case of a single cell within the multicellular system of the mouse early embryo.

The photodynamic effect, viz., photodamage of stained cells in the presence of oxygen, is used for destruction of tumors and other abnormal cells. The present review considers the biophysical mechanisms of the photodynamic action on cells. The importance of two major mechanisms of photodynamic damage of cells is discussed. The first one is mediated by electron or proton transfer, whereas the second one involves singlet oxygen. Another question that is considered is the importance of oxidation of membrane lipids or proteins for the photodynamic damage of cells. The phototransformation of photosensitizers and their intracellular localization and delivery to cells and tissues that have undergone abnormal changes are discussed. The current data on photosensitizer nanotransporters are presented. The potential sensors for reactive oxygen species in cells are discussed.

The mechanisms of synchronization have been studied in a mathematical model of the neurodynamics of navigation behavior that is based on even cyclic inhibitory networks. The following factors that affect the synchronized activity of the information units of the network have been highlighted: the weights of interunit connections, the duration of network activity, and the amplitude, duration, and timing of input signals.

A comparative study of the bioelectrical impedance of normotensive and hypertensive animal tissues was carried out. It was found that the electrical resistance of kidneys, lungs, and intercostal muscles in rats with arterial hypertension (ISIAH strain) was significantly lower than in normotensive Wistar rats, which indicates that the volume of circulating blood and the total amount of fluid were increased in animals with arterial hypertension. The fact that the resistance of the conducting medium is decreased in arterial hypertension should be taken into account in the analysis of cardioelectric potentials on the body surface and electrocardiograms in conventional leads, as well as for the purposes of the development of heterogeneous torso models and for verification of recovery algorithms for electrical properties of chest tissues.

This article concentrates on modeling the evolution of a population in a changing environment. We raise the optimization problem, which reflects the mechanisms of regulation of the speed of evolution that provide an adequate population response in correspondence with the direction and rate of environmental change. The numerical experiment results show plausible age–specific fertility dependences on the rate of environmental changes, as well as describing and explaining a number of evolutionary effects.

The authors expand the analysis of the so-called fractal of tripling periods manifested in various physical, geophysical, biophysical, and biological phenomena to demonstrate the adjustment of processes that occur in complex technical devices to the same pattern. As a result, an opportunity for significant improvement of the efficiency of design of such devices by a priori adjustment of the key periods to the periods of the fractal is revealed. The research on technical systems showed that the lower limit of the fractal of tripling periods lies in the microwave frequency range; therefore research on medical and healthcare applications of the phenomena observed appears to be relevant.