Zeitschrift fur Naturforschung. Section C, Biosciences最新文献

Monoterpene derivatives with spasmolytic activity inhibited acetylcholinesterase (ACHE, EC 3.1.1.7) in a dose dependent manner in vitro. The median inhibitory concentrations ranges between 10(-4) M and 10(-2) M. A significance of our finding may be the possible explanation of effects of monoterpene derivatives seen in distony of digestive tract.

The influence of Mg2+ ions on the secondary and tertiary structure of the RNA from bacteriophage MS2 was investigated by small-angle X-ray scattering and light scattering and by sedimentation experiments. The analysis of the outer part of the X-ray scattering curve obtained at low temperature in the absence of Mg2+ yielded a cross-section radius of gyration of 0.88 nm and a mass per unit length of 1720 g mol-1 nm-1. Very similar values for these parameters, which refer to the secondary structure of the RNA molecule, were also derived from the X-ray scattering curves obtained in the presence of different amounts of Mg2+ (0.07 to 1 ions per nucleotide). On the contrary, the inner part of the X-ray scattering curves turned out to be highly dependent on the Mg2+ concentration: the cross-section radius of gyration and the mass per unit length, which were determined from the scattering curves at small angles as parameters related to the tertiary structure of the RNA, amounted to 3.11 nm and 4000 g mol-1 nm-1, respectively, in the absence of Mg2+ and increased significantly upon raising the concentration of Mg2+. The increase of these structural parameters was found to be accompanied by a decrease of the overall radius of gyration (as revealed indirectly by X-ray scattering and directly by light scattering measurements) and by an increase of the sedimentation coefficient. The results from the investigations of the RNA at low temperature clearly establish the existence of double-stranded structures down to very low Mg2+ concentrations as well as the occurrence of Mg2+ induced changes of the tertiary structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Incubation of synaptosomal plasma membranes (SPM) with liposomes of phosphatidylserine (PS), phosphatidylinositol (PIN) or phosphatidylglycerol (PGL), led to an increase of acetylcholinesterase (AchE) activity at concentrations of 0.1-1 mumol phospholipids per mg SPM protein. The use of higher concentrations (1-7 mumol/mg protein), however, led to a progressive inhibition of the activity with respect to the maximal percentage of enzyme stimulation. To explain the enzyme stimulation by the acidic phospholipids, AchE was solubilized with the detergent Lubrol-PX and showed no change in the enzyme activity at any PS, PIN or PGL concentration used, indicating that these compounds do not act on the protein molecule directly. Arrhenius plots of AchE activities in untreated SPM (control), exhibited a break point at 23 degrees C, which was decreased to 16-17 degrees C in PS-treated SPM. Moreover, the Arrhenius activation energy (Ea) value in PS-treated SPM was increased related to the Ea below the break point in the control. These results indicate that acidic phospholipids do not act on AchE directly, but indirectly, affecting the membrane fluidity probably. Such modifications of interactions between lipid and AchE may control physiological processes in the central nervous system.

Ion exchange and affinity chromatography techniques, similar to those previously reported for purification of adenosine kinase from human placenta, were applied to purification of rat liver adenosine kinase. The enzyme, purified 400-fold in 41% yield, was homogeneous on SDS-polyacrylamide gel electrophoresis, with a molecular weight of 52000. It specific activity, 18 mumol/min/mg protein, is the highest hitherto reported for this enzyme from mammalian sources. Chromatography on DEAE-cellulose removed about 98% of the phosphorylating activity towards 2'-deoxyadenosine present in the initial pH-treated liver extract. The final preparation exhibited only minimal activity (approximately 1.5%) under optimal conditions (pH 7.5) vs 2'-deoxy-adenosine, the lowest yet reported for such a preparation, with a Km of 670 microM, as compared to 0.3 microM for adenosine. The residual activity towards deoxyadenosine is considered an intrinsic property of the purified adenosine kinase and, in fact, phosphorylation of adenosine was inhibited competitively by deoxyadenosine, with a Ki of 70 microM. Competitive inhibition was also exhibited by cordycepin (3'-deoxyadenosine) with a Ki of 150 microM. A more potent competitive inhibitor was tubercidin, the Ki for which was 1.9 microM.

The phospholipase C-activity in crude extracts of bovine blood platelets is strongly inhibited by the calmodulin-inhibitors fluphenazine and calmidazolium in the mM range, and activated by ATP and ADP, but not by AMP. The activating effect is also shown by the nonhydrolysable ATP- and ADP-analogs alpha,beta- and beta,gamma-methyleneadenosine 5'-triphosphate and alpha,beta-methyleneadenosine 5'-diphosphate, thus indicating that it is an allosteric effect. The stimulation of the phospholipase C-activity by ATP is also detectable in some partially purified fractions of the crude platelet extract, but it is abolished on further purification of the enzyme.

The influence of 5-heptadecenylresorcinol and total rye 5-alkenylresorcinols isolated from rye grains on the red blood cell water permeability was studied using osmotic shrinkage experiments performed in 300 mM sucrose. The studied compounds induced significant increase of erythrocyte water permeability. The threshold concentration needed for the increase of water permeability was in an order of 10(-6) mol/l. The temperature dependence of the observed process showed the discontinuity which was related to the 5-alkenylresorcinol transition temperatures. It was shown also that alkenylresorcinols did not exert the biphasic action on hypotonic lysis of erythrocytes usually observed for water soluble surfactants. The specific lysine activity is postulated for the studied compounds.

The fluorescence spectra of colonies of Propionibacterium acnes were studied under various experimental conditions. The spectra contained peaks at 580 nm and 620 nm. These bands were due to two different components; the 580 nm component was likely to be a metalloporphyrin, and there are indications that the 620 nm component could be a coproporphyrin. The 580 nm fluorescence was destroyed by the combined action of light and oxygen (no destruction under strict anaerobic conditions). A dark period interrupting the bleaching light stopped the destruction of this component for the time of the dark period. The initial production of the 620 nm component was due to the oxygen exposure. Upon light irradiation this component was later destroyed by the combined action of oxygen and light.

The response of yeast cells to different kinds of "stress" is not identical. Cells of the stationary growth phase synthesize three new proteins of molecular weights 68, 27 and 24 kD, compared with cells of the exponential growth phase, while heat-shocked cells exhibit new proteins of 100, 90, 84, 70 and 24 kD. After treatment with acrylonitrile two new proteins with molecular weights of 70 and 46 kD appear. However, all three kinds of "stress" lead to the induction of a ribonuclease.

In a simple phosphate buffer or a sodium chloride solution resting cells of Pseudomonas spec. DSM 2874 produced up to 15 g/l of different rhamnolipids. The rhamnolipid composition of the organic crude extract depended on the temperature during the cultivation and on the C-source. The optimal sodium chloride concentration for rhamnolipid formation was about 100 mM/l and the optimal phosphate buffer concentration about 65 mM/l. The optimal pH-value for the production of rhamnolipids from n-alkanes or glycerol was in the range pH 6.0-7.2. While rhamnolipid formation with glycerol as the sole C-source showed a wide optimum ranging from 27 degrees up to 37 degrees C, production of rhamnolipids from n-alkanes had a sharp optimum at 37 degrees C. The addition of multivalent cations, different N-sources and EDTA caused an inhibition of rhamnolipid formation, while the n-alkane concentration had no influence. Specific rhamnolipid formation decreased with increasing cell concentration. Various C-sources were suitable for the formation of rhamnolipids by resting cells of Pseudomonas spec. DSM 2874. Yields, which were comparable to those obtained on n-alkanes or glycerol, were found for stearic acid, fatty alcohols and vegetable oils. A study of the time course of glycolipid production of resting cells was carried out in a 20 1-bioreactor with an intensor system and with n-tetradecane as the sole C-source.

The effects of osmolarity, calcium concentration and cell-size liposomes in the subphase on the surface tension of phospholipid monolayers were investigated. The monolayers were spread from chloroform solutions of phosphatidic acid at air/water solution interface. The liposomes (of average diameter 3 micron) were formed from phosphatidic acid/egg lecithin (1:2) mixtures in water or 0.1 M water solutions of sucrose. For this system there were critical concentrations of calcium ions to produce a large reduction of the monolayer surface tension. The threshold calcium concentrations depended upon the sucrose concentration in the subphase. Without sucrose the threshold calcium concentration was 8 mM, while for isoosmotic sucrose solutions (0.1/0.1 M in/out of liposome) it was 14 mM. It sharply increased to 28 mM CaCl2 at sucrose concentration difference across the liposome membrane 0.02 M and decreased to 26 mM, 19 mM, and 18 mM with further increase of that difference to 0.04 M, 0.06 M, and 0.08 M, respectively. The rate of monolayer surface tension decrease was measured as a function of time at 30 mM CaCl2 and different sucrose concentrations in the subphase solution. The initial rates at first decreased with increasing the osmotic pressure and after that they increased. The minimum occurred at sucrose concentration gradient across the liposome membrane 0.02 M, i.e., at the point of maximum threshold calcium concentration required for large decrease of the monolayer surface tension. These facts may be explained by recent theories of dynamics of adhesion, instability and fusion of membranes modeled as thin films.