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81.
Different methods to estimate the plasma membrane potential difference (PMP) of yeast cells with fluorescent monitors were
compared. The validity of the methods was tested by the fluorescence difference with or without glucose, and its decrease
by the addition of 10 mM KCl. Low CaCl2 concentrations avoid binding of the dye to the cell surface, and low CCCP concentrations avoid its accumulation by mitochondria.
Lower concentrations of Ba2+ produce a similar effect as Ca2+, without producing the fluorescence changes derived from its transport. Fluorescence changes without considering binding
of the dyes to the cells and accumulation by mitochondria are overshadowed by their distribution between this organelle and
the cytoplasm. Other factors, such as yeast starvation, dye used, parameters of the fluorescence changes, as well as buffers
and incubation times were analyzed. An additional approach to measure the actual or relative values of PMP, determining the
accumulation of the dye, is presented. 相似文献
82.
Potential distribution of the invasive freshwater dinoflagellate Ceratium furcoides (Levander) Langhans (Dinophyta) in South America 下载免费PDF全文
Norma Meichtry de Zaburlín Roberto E. Vogler María J. Molina Víctor M. Llano 《Journal of phycology》2016,52(2):200-208
Dinoflagellates of the genus Ceratium are predominantly found in marine environments, with a few species in inland waters. Over the last decades, the freshwater species Ceratium hirundinella and Ceratium furcoides have colonized and invaded several South American basins. The purpose of this study was to create a distribution model for the invasive dinoflagellate C. furcoides in South America in order to further investigate the basins at potential risk, as well as the environmental conditions that influence its expansion. This species is known to develop blooms due to its mobility, resistance to sedimentation, and optimized use of resources. Although nontoxic, blooms of the species cause many problems to both the natural ecosystems and water users. Potential distribution was predicted by using a maximum entropy algorithm (MaxEnt). Model was run with 101 occurrences obtained from the scientific literature, and climatic, hydrological and topographic variables. The developed model had a very good performance for the study area. The most susceptible areas identified were mainly concentrated in the basins between southeastern Brazil and northeastern Argentina. Besides already affected regions, new potentially suitable areas were identified in temperate regions of South America. The information generated here will be useful for authorities responsible for water and watershed management to monitor the spread of this species and address problems related to its establishment in new environments. 相似文献
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Tyr 165 in the catalytic subunit of Escherichia coli aspartate transcarbamoylase (ATCase, EC 2.1.3.2) forms an intersubunit hydrogen bond in the T state with Glu 239 in the 240s loop of a second catalytic subunit, which is broken in the T to R transition. Substitution of Tyr 165 by Phe lowers substrate affinity by approximately an order of magnitude and alters the pH profile for enzyme function. We have determined the crystal structure of Y165F at 2.4 Å resolution by molecular replacement, using a wild-type T state structure as the probe, and refined it to an R value of 25.2%. The Y165F mutation induces a global conformational change that is in the opposite direction to the T to R transition and therefore results in an extreme T state. The two catalytic trimers move closer by ∼0.14 Å and rotate by ∼0.2°, in the opposite direction to the T→R rotation; the two domains of each catalytic chain rotate by ∼2.1°, also in the opposite direction to the T→R transition; and the 240s loop adopts a new conformation. Residues 229 to 236 shift by ∼2.4 Å so that the active site is more open. Residues 237 to 244 rotate by ∼24.1°, altering interactions within the 240s loop and at the C1-C4 and C1-R4 interfaces. Arg 167, a key residue in domain closure and interactions with L-Asp, swings out from the active site to interact with Tyr 197. This crystal structure is consistent with the functional properties of Y165F, expands our knowledge of the conformational repertoire of ATCase, and indicates that the canonical T state does not represent an extreme. Proteins 33:430–443, 1998. © 1998 Wiley-Liss, Inc. 相似文献
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Norma Espinoza-Herrera Ruth Pedroza-Islas Eduardo San Mart��n-Martinez Alfredo Cruz-Orea Sergio Armando Tom��s 《Food biophysics》2011,6(1):106-114
The proposal in this study was to evaluate the physical properties of different biopolymers films. The materials used were:
pectin, carboxyl methylcellulose, methylcellulose, hydroxyl propylcellulose, hydroxypropyl-methylcellulose, and corn waxy
starch; from these polysaccharides aqueous dispersions were prepared to 3% (w/v) for obtained films. In these biopolymer films, the thermal diffusivities (α) was evaluated by the Open Photoacoustic Cell
method; also, their mechanical properties as tensile strength, elongation, and Young’s modulus were measured, their crystallinity
percentage was evaluated by X-ray diffraction and microstructure through atomic force microscopy in contact mode. From the
polysaccharide films, it was observed that most of them were flexible and transparent. In the case of the films, mechanical
properties were found that the highest value of tensile strength and Young’s modulus corresponded to carboxyl methylcellulose
with 69.17 and 1,912.20 MPa values, respectively. Also, Open Photoacoustic Cell method and X-ray diffraction measurements
showed that there exist a correlation between the thermal diffusivity values and the crystallinity measured in the biopolymer
films. It was also observed that α values of cellulose derived was affected by the substitution group in the molecule, reaching
the highest α value, the films of carboxyl methylcellulose. Regarding the microstructural of the films, starch showed the
highest roughness value (88.6 nm) whereas hydroxypropyl-methylcellulose resulted with the lowest roughness value (7.67 nm). 相似文献
89.
Plasma membrane injury is a frequent event, and wounds have to be rapidly repaired to ensure cellular survival. Influx of Ca2+ is a key signaling event that triggers the repair of mechanical wounds on the plasma membrane within ~30 sec. Recent studies revealed that mammalian cells also reseal their plasma membrane after permeabilization with pore forming toxins in a Ca2+-dependent process that involves exocytosis of the lysosomal enzyme acid sphingomyelinase followed by pore endocytosis. Here, we describe the methodology used to demonstrate that the resealing of cells permeabilized by the toxin streptolysin O is also rapid and dependent on Ca2+ influx. The assay design allows synchronization of the injury event and a precise kinetic measurement of the ability of cells to restore plasma membrane integrity by imaging and quantifying the extent by which the liphophilic dye FM1-43 reaches intracellular membranes. This live assay also allows a sensitive assessment of the ability of exogenously added soluble factors such as sphingomyelinase to inhibit FM1-43 influx, reflecting the ability of cells to repair their plasma membrane. This assay allowed us to show for the first time that sphingomyelinase acts downstream of Ca2+-dependent exocytosis, since extracellular addition of the enzyme promotes resealing of cells permeabilized in the absence of Ca2+. 相似文献