Biofizika最新文献

Based on the analysis of changes in the local density of the insect within the family Psillidae in Australia we have developed a model for a scenario of a dramatic increase in the number of jumping plant lice at the expense of primary and secondary Encyrtidae parasitoid microwasps. A phenomenological model describes on a case by case basis the efficiency of reproduction in several ranges of population conditions. We have proposed a continuous-event structure, where the rate of a decrease of the number of psyllid generations is uneven at different stages of ontogenesis of the insect with an incomplete metamorphosis. The moments when the rate is changing are determined by the state of internal variables of the auxiliary equation of a continuous system. Spontaneous time-limited local outbreak occurs after overcoming the threshold balancing in iterative dynamic system that reduces the effect of normal regulatory mechanisms of psyllid reproduction and the speed of a decrease of the number of generations changes. The method with the addition of the right side of the first equation by special functionality with limited range of values simulates a sharp decrease in survival with the exhaustion of resources. The limited availability of leaves causes a backward tangent bifurcation. After a few iterations from the tangent bifurcation population transfers to the mode of ordinary fluctuations without explicit of cyclical component at a low average psyllids population.

With the direct labeling procedure for detecting DNA fragmentation we explored the influence of the different storage temperature conditions as well as different methods of cryopreservation on the structure of DNA organization in the human sperm. 19 sperm samples obtained from healthy men with normozoospermia (according to the criteria of the World Health Organization) were used for investigation. A significant increase of human sperm DNA-fragmentation was observed after 8 hours of incubation at +39 degrees C (by 76.7%) and at +37 degrees C (by 68.9%). It was found that sperm cooling with the use of a cryoprotectant immediately after thawing did not produce significant differences in the extent of DNA fragmentation, although samples, containing cryoprotectants, showed a sharp increase of DNA fragmentation after 24 hours of incubation, that could suggest cryoprotectant cytotoxicity.

The molecular dynamics method has been applied to investigate the conformational behavior of biologically important chiral molecules of cholesterol and ergosterol. The formation of strings in the solution of cholesterol in methanol and the lack of strings in solutions of ergosterol in methanol has been experimentally detected. It was shown that the intermolecular dynamics in the molecule has a significant impact on the potential of structure formation. We proposed alternative explanation of the functional significance of cholesterol, apparently associated with the formation of interconnect structures outside the membrane as the biological feasibility of finding ergosterol in non-switched cells of fungi and cholesterol in the switching cells of macroorganisms.

The binding of distamycin dimeric analog (Pt-bis-Dst) to poly[d(A-T)] x poly[d(A-T)1, poly(dA) x poly(dT) and duplex O23 with the sequence 5'-GCCAATATATATATATTATTAGG-3' which is present at the origin of replication of herpes simplex virus OriS is investigated with the use of UV and CD spectroscopy. The distinction of the synthetic polyamide from a natural antibiotic lies in the fact that in the synthetic polyamide there are two distamycin moieties bound via a glycine cis-diamino platinum group. It was shown that the binding of Pt-bis-Dst to poly[d(A-T)] x poly[d(A-T)] and poly(dA) x poly(dT) reaches saturation if one molecule of the ligand occurs at approximately every 8 bp. With further increase in the ratio of the added ligand to the base pairs in CD spectra of complexes with poly[d(A-T)] x poly[d(A-T)], we observed that the maximum wavelength band tend to be shifted towards longer wavelengths, while in the spectral region of 290-310 nm a "shoulder", that was absent in the spectra of the complexes obtained at low polymer coverages by the ligand, appeared. At high molar concentration ratios of ligand to oligonucleotide Pt-bis-Dst can bind to poly[d(A-T)] x poly[d(A-T)] in the form of hairpins or may form associates by the interaction between the distamycin moieties of neighboring molecules of Pt-bis-Dst. The structure of the complexes is stabilized by interactions between pirrolcarboxamide moieties of two molecules of Pt-bis-Dst adsorbed on adjacent overlapping binding sites. These interactions are probably also responsible for the concentration-dependent spectral changes observed during the formation of a complex between Pt-bis-Dst and poly[d(A-T)] x poly[d(A-T)]. Spectral changes are almost absent in binding of Pt-bis-Dst to poly(dA) x poly(dT). Binding of Pt-bis-Dst to duplex O23 reaches saturation if two ligand molecules occur in a duplex that contains a cluster of 18 AT pairs. With increasing the molar concentration ratio of the ligand to the duplex CD spectra undergo concentration-dependent changes similar to those observed during binding of Pt-bis-Dst to poly [d(A-T)] x poly[d(A-T)]. Testing for antiviral efficacy of Pt-bis-Dst showed that the concentration, at which the cytopathic effect produced by the herpes simplex virus in cell culture Vero E6 halved, is equal to 1.5 μg/ml and the selectivity index for evaluating antiviral activity is 65 at a relatively low cytotoxicity. The concentration of Pt-bis-Dst, at which approximately half the cells are killed, is equal to 100 μg/ml.

Osmolytes are molecules with the function among others to align hydrostatic pressure between intracellular and extracellular spaces. Accumulation of osmolytes occurs in the cell in response to stress caused by pressure change, change in temperature, pH, and concentration of inorganic salts. Osmolytes can prevent native proteins denaturation and promote folding of unfolding proteins. Investigation of the osmolytes effect on these processes is essential for understanding the mechanisms of folding and functioning of proteins in vivo. A score of works, devoted to the effect of osmolytes on proteins, are not always consistent with each other. In this review an attempt was made to systemize available array of data on the subject and consider the problem of folding and stability of proteins in solutions in the presence of osmolytes from the single viewpoint.

The changes in structure and catalytic properties of fungal lipases (Candida rugosa, Rhizomucor miehei, Mucor javanicus) were investigated in micellar solutions of bile salts that differ in hydrophilic-lypophilic balance and reaction medium properties. The methods of circular dichroism and tryptophan fluorescence were applied to estimate the changes in peptide structure within complexes with bile salt micelles. Bile salts do not exert a significant influence on the structure of the enzymes under study: in Rh. miehei and M. javanicus lipases the alpha helix content slightly decreased, the influence of bile salts on the C. rugosa structure was not revealed. Despite negligible structural modifications in the enzymes, in bile salt solutions a considerable change in their catalytic properties was observed: an abrupt decrease in catalytic effectiveness. Substrate-bile salts micelles complex formation was demonstrated by the NMR self-diffusion method. The model of a regulation of fungal lipase activity was proposed.

It has been shown that hypoxia (5% 02) and fibroblast growth factor bFGF reduce the doubling time of bone marrow mesenchymal stem cells under their cultivation in vitro that indicates an increase in cell culture proliferation. It has been found out that low concentrations of O2 and factor bFGF added to the cell culture medium increase an expression of abcg2 gene and its gene protein, ABCG2 transport gene, in mesenchymal stem cells. These events potentiate the effects of hypoxia observed in mesenchymal stem cells. We revealed that blocking of ABCG2 protein functional activity led to increased generation of reactive oxygen species in mesenchymal stem cells. The effect of hypoxia and/or bFGF on protein profile of mesenchymal stem cells was studied. The results represented in this work together with previous data proved a link between ABCG2 protein expression, its activity and maintenance of viability and proliferative activity of mesenchymal stem cells cultivated under hypoxia. ABCG2 acts as protector.

This work presents the results of the analysis of the fluorescence lifetime of tryptophan in three proteins: human serum albumin, bovine serum albumin and bacterial luciferase, containing 1, 2 and 7 tryptophan residues, respectively. It was shown that for all proteins fluorescence decay can be fitted by three lifetimes: τ1 = 6-7 ns, τ2 = -2,0-2,3 ns and τ3 ≤ 0,1 ns (the native state) and τ1 = 4,4-4,6 ns, τ2 = 1,7-1,8 ns and τ3 ≤ 0,1 ns (the denaturated state). It was found that spectral profiles with individual protein fluorescence lifetime have similar peak wavelength and identical half-width of the spectrum as in the native state (λ(max)τ1 = 342 nm, λ(max)τ2 = 328 nm and λ(max)τ3 = 3i5 nm), and in the denaturated state (λ(max)τ1 = 350 nm, λ(max)τ2 = 343 nm and λ(max)τ3 = 317 nm). In addition, the differences in the steady-state spectra of the studied proteins are caused by the individual ratio of lifetime contributions. The correlation between. lifetime components and a known classification of the tryptophan residues in the structure of proteins, under study was performed within the discrete states model.

A model describing the process of dissociation of hydrogen bonding in water clusters when irradiated by electromagnetic field in the microwave range is suggested. The model is also applicable for the case of rupture of the covalent bond of the water molecule cluster. If the energy absorption occurs at the interface of water and polymer clusters (e.g., DNA, chitosan), degradation of the polymer chain is possible.

Aminoacyl-tRNA synthetases are an ancient enzyme family that specifically charge a tRNA molecule with a cognate amino acid required for protein synthesis. Glycyl-tRNA synthetase is one of the most interesting aminoacyl-tRNA synthetases due to its structure variability and functional features in the different organisms. It was shown recently that human glycyl-tRNA synthetase is a regulator of translational initiation of poliovirus mRNA. Details of this process and its mechanism still remain unknown. While exploring this stage of poliovirus functioning we have studied the interaction of the cytoplasmic form of human glycyl-tRNA synthetase and its domains with the fragments of the poliovirus IRES element. As a result, we have identified the minimal fragment of viral mRNA with which glycyl-tRNA synthetase fully interacts and estimated the contribution of some domains to the interaction of glycyl-tRNA synthetase with RNA.