Oxygen surface exchange kinetics of Ba0.5Sr0.5Co0.8Fe0.2O3-δ.

The mechanism of oxygen exchange between the gas phase and Ba0.5Sr0.5Co0.8Fe0.2O3-δ oxide was evaluated by considering the inhomogeneity of the oxide surface. The applicability of existing models for the analysis of the oxygen exchange mechanism was considered. A new model with a dissociation step was suggested. The rate-determining steps of the oxygen exchange process were revealed under different experimental conditions. The change in the rate-determining step occurred at 600-650 °C. The probable cause was considered taking into account the parameter of nonequivalency of adsorption centers. A relationship between the oxygen isotope redistribution rates and the rates of the elementary steps in a "gas phase-solid oxide" system was revealed.

Oxygen isotope exchange in La2NiO(4±Î´).

Oxygen surface exchange kinetics and diffusion have been studied by the isotope exchange method with gas phase equilibration using a static circulation experimental rig in the temperature range of 600-800 °C and oxygen pressure range of 0.13-2.5 kPa. A novel model which takes into account distributions of the dissociative adsorption and incorporation rates has been developed. The rates of the elementary stages have been calculated. The rate-determining stages for a La2NiO(4±Î´) polycrystalline specimen have been discussed. The diffusion activation energies calculated using the gas phase equilibration method (1.4 eV) differ significantly from those calculated using isotope exchange depth profiling (0.5-0.8 eV), which was attributed to the influence of different oxygen diffusion pathways.

Oxygen nonstoichiometry, defect structure and oxygen diffusion in the double perovskite GdBaCo2O6-δ.

Oxygen nonstoichiometry of GdBaCo2O6-δ was studied by means of the thermogravimetric technique in the temperature range 600-1000 °C. The defect structure model based on the simple cubic perovskite GdCoO3-δ was shown to be valid for GdBaCo2O6-δ up to temperatures as low as 600 °C. Two independent methods, namely dc-polarization with the YSZ microelectrode and (18)O-isotope exchange with gas phase analysis, were used to determine the oxygen self-diffusion coefficient in the double perovskite GdBaCo2O6-δ. All measurements were carried out using ceramic samples identically prepared from the same single phase powder of GdBaCo2O6-δ. The experimental data on oxygen nonstoichiometry of GdBaCo2O6-δ allowed a precise calculation of the oxygen interphase exchange rate and the oxygen tracer diffusion coefficient on the basis of the isotope exchange measurements. The values of the oxygen self-diffusion coefficient measured by the dc-polarization technique were found to be in very good agreement with the ones of the oxygen tracer diffusion coefficient.

[Somatotype of women of the Stavropol region with mammary gland pathology].

The aim of this study was to determine the somatotypic characteristics of women living in Stavropol region, both healthy persons and patients with mammary cancer. 105 women of second period of mature age and of eldery age were examined. For somatotype assessment the scheme of V.P. Chtetzov et al. (1979) was used. Age peculiarities of morphological typing were demonstrated that revealed the dominance of athletic type in mature age and mesoplastic type in the elderly one. The analysis of anthropometric parameters of women with oncological pathology in the indicated periods of ontogenesis has demonstrated a predominance of a mesomorphic vector in shaping their somatotype. The marker signs possessing the greatest informative value in mammary cancer patients of a second period of mature age were the low values of thickness of brachial and breast adipose folds. These signs are suggested as criteria for the formation of groups of risk.

[Role of the energy status of Escherichia coli in cell membrane phospholipid composition changes during aerobic-anaerobic transitions]. / Rol' énergeticheskogo statusa Escherichia coli v izmenenii fosfolipidnogo sostava kletochnykh membran pri aérobno-anaérobnykh perekhodakh]

The aerobic to anaerobic transition of E. coli is accompanied with interrelated changes of the adenylate pool, energy charge, respiration rate, as well as the phospholipid content of the cell membranes and the activity of the polyamine synthesizing system. The role of the cellular energy status in the control of the relative content of membrane phospholipids is discussed. The control is based either on energy redistribution in phospholipid metabolism or on the effect on the activity of the polyamine synthesizing system.

[The determination of phospholipase activity using the 31P-NMR spectroscopic method]. / Opredelenie aktivnosti fosfolipazy s metodom 31P-IaMR spektroskopii.

The authors have developed a rather rapid and convenient method for testing and measurement of phospholipase C (EC 3.1.4.3) activity, based on continuous recording of the signal reduction in 31P-NMR spectrum of lecithin phosphate group (chemical sigma shift = 0.2 parts per million as regards H3PO4) or of phosphocholine signal augmentation (sigma = -4 parts per million). This method permits a quantitative estimation of lecithin loss or phosphocholine accrual from the kinetics of integral intensity changes in the course of an enzymic reaction and then calculate phospholipase C activity without resorting to thin-layer chromatography traditionally used for this purpose.

[Comparative characteristics of the metabolism of E. coli cells with various activity of penicillin acylase]. / Sravnitel'naia kharakteristika metabolizma kletok E. coli s razlichnoi aktivnost'iu penitsillinatsilazy.

A correlation between the synthesis and secretion of penicillin acylase (PA; EC 3.5.1.11) and the membrane phospholipid composition was observed in three E. coli strains. In cells with overproduction of PA, the phospholipid/protein ratio decreases, while the cardiolipin/phosphatidylglycerol ratio increases. The differences in the functioning of the electron transport system were revealed in cells with different levels of PA synthesis and secretion. The O2 consumption rate was 3 times lower in the cells with overproduction of PA than in those of less productive strains. On the contrary, membrane particles isolated from the cells of PA producers had no significant differences in the O2-reduction rate. The sensitivity of the strains to the inhibitor of terminal oxidases, sodium cyanide, and to the uncoupler of redox phosphorylation, chlorocarbonyl-phenylhydrazone, was different. Thus the E. coli cells with PA overproduction are characterized by significant changes in energetics and constructive metabolism. The interrelations between PA overproduction, phospholipid metabolism and the respiratory chain activity are discussed.

[The cell wall of Bacillus brevis producing gramicidin S, a cyclodecapeptide antibiotic]. / Issledovanie obolochki Bacillus brevis--produtsenta tsiklodekapeptidnogo antibiotika gramitsidina S.

Gramicidin S is tritiated in Bacillus brevis G.-B. intact cells by activated tritium atoms (which is indicative of its surface localisation). The cell wall protein is tritiated very weakly, which shows that it is screened, apparently, by gramicidin adsorbed on its surface. The cell wall protein is not a glycoprotein and its interaction with exogenous gramicidin S causes cell aggregation. As follows from the Rf value after the chromatographic separation of B. brevis lipids, the reaction of staining, and the data of H-NMR spectroscopy for the fraction of phospholipids, the main membrane phospholipid is an anionic acetylated phosphatidyl ethanolamine.

[The membrane apparatus of Staphylococci in relation to acquired novobiocin resistance]. / Membrannyi apparat stafilokokkov v sviazi s priobreteniem ustoichivosti k novobiotsinu.

The properties of the membrane respiration apparatus of three clinical staphylococcal strains and their novobiocin resistant variants were studied comparatively. Changes in the specific activity of the respiration enzymes were shown: when the dehydrogenase activity of the membrane preparations of the sensitive and resistant variants was equal and the specific quantity of cytochromes in the novobiocin resistant staphylococci was lower, the oxidase activity of their respiration chains was increased by 60-70 per cent. Disintegration of the cells of the novobiocin resistant staphylococci resulted in a higher yield of the membrane protein, the membrane fraction being characterized by a activity of phospholipase A.

[Modification of the lipid component of bacterial membranes by the introduction of lipotropic compounds into lyophilized cells]. / Modifikatsiia lipidnogo komponenta bakterial'nykh membran putem vvedeniia lipotropnykh soedinenii v liofilizirovannye kletki.

In order to elucidate potentialities of modifying the lipid component of bacterial membranes, lyophilized cells of M. lysodeikticus, E. coli and other bacteria were treated by hydrophobic compounds dissolved in the organic solvent, with the latter subsequently removed by evaporation or freezedrying prior to cell rehydration. The data obtained by means of spin-probes, fluorescent spectroscopy, electron microscopy, photoreactive label and other methods suggest that following bacteria rehydration at least part of the substance occurs in the membrane structures. The amount of the substance involved in bacterial cells depends on the type of compound and on whether bacterial cells belong to gram-positive or gram-negative microorganisms: the substance content of the latter is greater than of the former.

[Constructive and energy metabolism changes in the formation and germination of resting retractile forms of Bacillus cereus]. / Izmeneniia konstruktivnogo i énergeticheskogo metabolizma v protsesse obrazovaniia i prorastaniia pokoiashchikhsia refraktil'nykh form Bacillus cereus.

It has been found that, as soon as Bacillus cereus vegetative cells yield resting refractile forms under the action of specific autoregulating factors, the incorporation of labeled precursors of the main cellular biopolymers and lipids stops almost entirely and the level of cell endogenous respiration abruptly decreases. When the refractile forms revert to the vegetative state and growth, the processes of biosynthesis and respiration are restored. The level of metabolism typical of vegetative cells of the control cultures is reached within 90 min.

[Compartmentation of gramicidin 5 in membranes of sensitive bacteria and protein-lipid interactions]. / Raspolozhenie gramitsidina S v membranakh chuvstvitel'nykh k nemu bakterii i belok-lipidnye vzaimodeistviia.

Gramicidin S is sorbed on the isolated membranes of granicidin-sensitive Micrococcus lysodeikticus strain. The antibiotic inhibits the membrane malate dehydrogenase within the temperature range of 9--42 degrees C, i.e. under conditions of gel and liquid-crystalline lipid state; however its effect at 10 degrees C is 10 times as low as is observed at 42 degrees C. The inhibitory effect of gramicidin S on malate dehydrogenase can be eliminated and the antibiotic can be removed from the membrane by an excess of different phospholipids. No transfer of the membrane components on exogenous phospholipids is observed. A prolonged (about 2 hrs, 30 degrees C) incubation of the membranes with gramicidin S results in irreversible inactivation of malate dehydrogenase, although the antibiotic can be still eliminated by an addition of phospholipid emulsions. It is suggested that gramicidin S forms complexes with phospholipids, in which the antibiotic is oriented to water. These complexes disturb the lipid-protein interactions, resulting in relaxation of the binding between the boundary phospholipids and proteins, in the loosening of near-protein lipid zones and simultaneous condensation of acid phospholipids in the whole membrane. Destruction of the lipid zone is accompanied by changes in the enzyme activity, by separation of lipid and protein regions and by transphase enzyme transitions (expulsion or immersion). A slow formation of secondary protein-protein associates may be irreversible.