Membrane mechanisms of testosterone action]

The experiments on adult Wistar rats have shown that testosterone administration provoke hyperpolarization of hepatocytes and adrenocorticocytes plasmatic membranes. It was discovered that this hyperpolarization was caused by cell Na, K-ATPase activation. Inhibitors of protein biosynthesis prevent both testosterone-induced hyperpolarization and Na, K-ATPase activation. It is shown that some hyperpolarization factor appeared in the cytosol and blood serum under testosterone influence. It was suggested that this mechanism is mediated by cell genome.     

Combined action of ultrasound and ionizing radiation on yeast cells

Summary This communication reports the observation of synergistic relationships between ultrasound and gamma-irradiation of stationary phase cultures ofSaccharomyces cerevisiae of different strains. The gamma-ray dose was applied before or after the sound. The extent of synergism depended upon the sequence of application; it was smaller for (US +-ray)-exposure in comparison with (-ray + US)-treatment. The combined action of both modalities had smaller or no synergistic effect for mutant (rad51) yeast cells incapable of recovery. On this basis, it was concluded that possible mechanisms for ultrasound radiosensitization of yeast cells may involve the reduced capacity of cells to recover damages resulted from the combined action and/or the enhanced expression of lethal damage.     

Sorptive affinity of ionic surfactants on silt loamy soil

Due to their broad applications, ionic surfactants have already been released into or utilized in soil and environmental systems. However, current understanding on the sorption behavior of surfactants onto soils is still limited. This work systematically investigated the sorption kinetics and isotherms of one cationic surfactant, cetyltrimethylammonium bromide (CTAB), and one anionic surfactant, sodium dodecyl sulfate (SDS), onto a silt loamy soil to determine the governing sorption mechanisms. The pseudo-second-order rate equation described the sorption kinetics data better than the pseudo-first-order rate equation. Experimental data showed that the sorption equilibrium for CTAB and SDS were reached at 24 and 240 h, respectively. Langmuir equation was better than Freundlich equation in simulating the sorption isotherms of CTAB and SDS on the soil. Soil Langmuir maximum sorption capacity of CTAB was much higher than that to SDS. When the experimental temperature increased, the sorption of CTAB and SDS on the soil decreased. In addition, the sorptive process of the surfactants on the soil was spontaneous and exothermal, as indicated by the absolute values of Gibbs free energy and enthalpy. The results also indicated that physical sorption was the dominant mechanism for the sorption of the two surfactants on the soil. Findings from this work are crucial to understand the environmental behaviors of ionic surfactants.     

Features of action of low doses of gamma-radiation on yeast cells

Lethal effect of low doses and adaptive response to low doses of prolonged irradiation were investigated in experiments on yeast cells. The phenomenon of hypersensitivity at low dozes was not found in yeast cells at gamma-irradiation. The adaptive response was observed after exposure to low doses of prolonged irradiation, the degree of the reaction depends on a dose rate. The adaptive reaction was kept for some time after the termination of adaptive irradiation then the sensitivity of cells increased even in comparison with unirradiated ones.     

Influence of cations on the mode of action of miconazole on yeast cells

The influence of the antifungal agent miconazole nitrate on yeast plasma membranes was studied in a concentration range 0-100 microM. The reaction of 100 microM miconazole with the plasma membranes lead to a rapid breakdown of the transmembrane pH gradient and to an efflux of metabolites from the cytoplasm of the cells. This effect of miconazole could be reversed by mono-, di- and most effectively by trivalent cations due to the formation of miconazole-cation complexes. At a ratio of trivalent cation/miconazole (1:3) the effect was completely reversed. X-Ray diffraction studies indicated a crystalline structure of the aluminium-miconazole complex.     

多巴胺对PC12细胞的双重影响

本实验运用PC12细胞,研究不同浓度多巴胺（dopamine,DA)对细胞的影响,同时利用兼具促进多巴胺释放和抑制多巴胺摄取双重作用的安排它命（amphetamine,AMP)观察胞内外多巴胺对细胞的不同作用。结果显示;胞外高浓度DA能引起细胞抗氧化能力下降,胞内游离Ca^2 浓度上升。细胞存活率大幅度降低,部分细胞出现凋亡;低浓度DA对细胞存活率无明显影响,而使细胞抗氧化能力有一定提高,长时间安非它命单独作用也可引起细胞存活率下降,并伴随胞内GSH水平降低;安非它命与多巴胺共同作用在一定程度上可导致细胞内抗氧化物质水平低于多巴胺单独作用,表明细胞内一定浓度DA可以维持或提高细胞抗氧化物质水平。结果提示,脑内同样存在的多巴胺神经元对DA重摄取功能下降,胞外氧化应激增强,可能是引起脑内多巴胺神经元退行性病变的重要原因之一。     

Dielectric properties of yeast cells: Effect of some ionic detergents on the plasma membranes

Summary Dielectric measurements were made on suspensions of yeast cells treated with two homologous series of sodium alkyl (C₈, C₁₀, C₁₂, C₁₄) sulfonates and alkyl (C₈, C₁₀, C₁₂, C₁₄, C₁₆, C₁₈) benzyl dimethyl ammonium chlorides over a frequency range of 10 kHz to 100 MHz. Dielectric dispersions observed for the suspensions of intact yeast cells are found to be reduced by treatment with these detergents, the reduction being accompanied by a decrease in packed volume of the cells and by a leakage of intracellular compounds. The reduction of dielectric dispersions is considered to be caused by a decrease in volume of the cells in suspensions and an increase in conductivity of the cell membranes. An effect of the alkyl chain length of the detergents on the reduction of dielectric dispersions is also examined for these ionic detergents. The reducing effect shows the maximum at the alkyl chain, C₁₄ for sodium alkyl sulfonates and at C₁₆ for alkyl benzyl dimethyl ammonium chlorides. These results are consistent with hemolysis and bactericidal activity.     

Serine proteinase from Bacillus brevis: lytic action on intact yeast cells

Summary A serine proteinase which showed lytic acitivity against either intact cell or cell wall preparations of Candida utilis has been isolated from Bacillus brevis culture filtrate by affinity chromatography on bacitracin-silochrome and phenylboronale-Sepharose. Both its proteolytic and lytic activities were completely abolished by inhibitors of serine proteinases, including phenylmethylsul-phonylfluoride, the inhibitor from Actinomyces janthinus, and duck ovomucoid. The optimum pH range for the enzyme is 7.5–9.0, the optimum temperature 40°–50°C, its pI value 8.6 and motecular weight 28000. The amino acid composition of this proteinase is similar to that of serine proteinase from B. amyloliquefaciens (subtilisin BPN), its N-terminal amino acid sequence being identical to that of BPN through 21 residues. The enzyme cleaves chromogenous substrates for subtilisins but shows no activity on a substrate for trypsin. By means of both turbidimetry and electron microscopy the enzyme studied was shown to cause yeast cell lysis.     

Membrane potential in yeast cells measured by direct and indirect methods

The membrane potential, ΔΨ, of various yeasts estimated from the distribution of tetraphenylphosphonium cations ranged from ?50 to ?120 mV, depending on species, incubation conditions and technique of measurement. Values obtained directly with a microelectrode in Endomyces magnusii were consistently lower than those determined indirectly.     

Modulating enzyme activity using ionic liquids or surfactants

One of the important strategies for modulating enzyme activity is the use of additives to affect their microenvironment and subsequently make them suitable for use in different industrial processes. Ionic liquids (ILs) have been investigated extensively in recent years as such additives. They are a class of solvents with peculiar properties and a "green" reputation in comparison to classical organic solvents. ILs as co-solvents in aqueous systems have an effect on substrate solubility, enzyme structure and on enzyme–water interactions. These effects can lead to higher reaction yields, improved selectivity, and changes in substrate specificity, and thus there is great potential for IL incorporation in biocatalysis. The use of surfactants, which are usually denaturating agents, as additives in enzymatic reactions is less reviewed in recent years. However, interesting modulations in enzyme activity in their presence have been reported. In the case of surfactants there is a more pronounced effect on the enzyme structure, as can be observed in a number of crystal structures obtained in their presence. For each additive and enzymatic process, a specific optimization process is needed and there is no one-fits-all solution. Combining ILs and surfactants in either mixed micelles or water-in-IL microemulsions for use in enzymatic reaction systems is a promising direction which may further expand the range of enzyme applications in industrial processes. While many reviews exist on the use of ILs in biocatalysis, the present review centers on systems in which ILs or surfactants were able to modulate and improve the natural activity of enzymes in aqueous systems.