Showing papers by "University of Extremadura published in 1985"
TL;DR: It is concluded that neither dihydroneopterin triphosphate, nor one of its metabolites are of primary importance for an immune reaction.
46 citations
TL;DR: The mitotic patterns and cytoarchitecture of the optic stalk were studied in the chick embryo during the period of formation of the optics cup until the elimination of the stalk lumen, favouring invasion of the ventral stalk by optic fibers and the addition of new glioblasts by proliferation of preexisting cells.
Abstract: The mitotic patterns and cytoarchitecture of the optic stalk were studied in the chick embryo during the period of formation of the optic cup until the elimination of the stalk lumen. Cell proliferation in the superficial regions of the stalk ventral wall is described. Superficial cell proliferation, whose beginning coincides with penetration of the earliest optic fibers, gives rise to an early glioblast plate located internally with respect to the marginal lamina of ganglion cell axon fascicles. The early glioblasts are transformed into marginal glioblasts, which undergo radial mitosis. Radially oriented division seems to favour glioblast penetration towards more internal zones of the stalk. Thus the marginal glioblasts are transformed into inner glioblasts, which continue to proliferate. Cell death in the ventral wall of the optic stalk is in close topographical relation with extracellular spaces which loosen up the consistency of the stalk tissue, favouring invasion of the ventral stalk by optic fibers and the addition of new glioblasts by proliferation of preexisting cells.
29 citations
TL;DR: Transmission electron microscopic studies show that both in the chick and in the duck, interdigital blood vessels are immature structures lacking basal lamina, and the possible relationships between interdigital mesenchymal cell death and vascular regression are discussed.
Abstract: The pattern and structure of the blood vessels of the interdigital spaces of the leg bud have been studied by means of Indian ink injections and transmission electron microscopy in the chick and duck embryos. The results show that in the chick the interdigital necrotic process responsible for the freeing of the digits is followed by regression of the blood vessels. In the webbed foot of the duck, the interdigital necrotic processes are not followed by vascular regression. Transmission electron microscopic studies show that both in the chick and in the duck, interdigital blood vessels are immature structures lacking basal lamina. Dead cells of presumably endothelial origin were detected in the lumen of the regressing blood vessels of the chick but not in the duck. However, the intensity of this cell death process does not appear to be high enough to account by itself for the disappearance of the interdigital blood vessels. The possible relationships between interdigital mesenchymal cell death and vascular regression are discussed.
28 citations
TL;DR: Studies in continuous culture indicate a strong relationship between the synthesis of exoglucanase activity and the specific growth rate and are taken as evidence of an essential role of this activity during the yeast budding cycle.
Abstract: The rate of synthesis and secretion of exo-1–3-β-glucanase activity closely paralleled the specific rate of growth in exponentially growing Saccharomyces cerevisiae cells in batch culture. When the stationary phase was reached both synthesis and secretion stopped. No activity was synthesized when the cells were maintained in carbon sources that did not allow them to grow. Studies in continuous culture indicate a strong relationship between the synthesis of exoglucanase activity and the specific growth rate. These results are taken as evidence of an essential role of this activity during the yeast budding cycle.
23 citations
TL;DR: The hypothesis attributing the redox interconversion to formation/disappearance of an erroneous disulfide between one of the half-cystines located at the GSSG-binding site and another cysteine nearby is supported.
Abstract: 1
The changes undergone by pure yeast glutathione reductase during redox interconversion have been studied. Both the active and inactive forms of the enzyme had similar molecular masses, suggesting that the inactivation is probably due to intramolecular modification(s).
2
The glutathione reductase and transhydrogenase activities were similarly inactivated by NADPH and reactivated by GSH, while the diaphorase activity remained unaltered during redox interconversion of glutathione reductase. These results suggest that the inactivation site could be located far from the NADPH-binding site, although interfering with transhydrogenase activity, perhaps by conformational changes.
3
The inactivation of glutathione reductase by 0.2 mM NADPH at pH 8 was paralleled by a gradual decrease in the absorbance at 530 nm and a simultaneous increase in the absorbance at 445 nm, while the reactivation promoted by GSH was initially associated with reversal of these spectral changes. The inactive enzyme spectrum retained some absorbance between 500 nm and 700 nm, showing a shoulder at 580–600 nm. Upon treatment of the enzyme with NADPH at pH 6.5 the spectrum remained unchanged, while no redox inactivation was observed under these conditions. It is suggested that the redox inactivation could be associated with the disappearance of the charge-transfer complex between the proximal thiolate and oxidized FAD in the two-electron-reduced enzyme.
4
The inactive enzyme was reactivated by low GSSG concentrations, moderate dithiol concentrations, and high monothiol concentrations. These results and the spectral changes described above support the hypothesis attributing the redox interconversion to formation/disappearance of an erroneous disulfide between one of the half-cystines located at the GSSG-binding site and another cysteine nearby.
23 citations
TL;DR: The glutathione reductase from E. coli was rapidly inactivated following aerobic incubation of the pure and cell-free extract enzymes with NADPH, NADH and other reductants, and was reactivated by treatment with oxidized and reduced glutATHione, ferricyanide, and dithiothreitol in a time-and temperature-dependent process.
Abstract: The glutathione reductase from E. coli was rapidly inactivated following aerobic incubation of the pure and cell-free extract enzymes with NADPH, NADH and other reductants. The inactivation of the pure enzyme depended on the time and temperature of incubation (t1/2 = 2 min at 37°C), and was proportional to the |INADPH|/|enzyme| ratio, reaching 50% in the presence of 0.3 μM NADPH and 45 μM NADH respectively, at a subunit concentration of 20 nM. Higher pyridine nucleotide concentrations were required to inactivate the enzyme from cell-free extracts. Two apparent pKa, corresponding to pH 5.8 and 7.3, were determined for the redox inactivation. The enzyme remained inactive even after eliminating the excess NADPH by gel chromatography.
E. coli glutathione reductase was protected by oxidized and reduced glutathione against redox inactivation with both pure and cell-free extract enzymes. Ferricyanide and dithiothreitol protected only the pure enzyme, while NADP+ exclusively protected the cell-free extract enzyme. The inactive glutathione reductase was reactivated by treatment with oxidized and reduced glutathione, ferricyanide, and dithiothreitol in a time-and temperature-dependent process. The oxidized form of glutathione was more efficient and specific than the reduced form in the protection and reactivation of the pure enzyme. The molecular weight of the redox-inactivated E. coli glutathione reductase was similar to that of the dimeric native enzyme, ruling out aggregation as a possible cause of inactivation. A tentative model is discussed for the redox inactivation, involving the formation of an ‘erroneous’ disulfide bridge at the glutathione-binding site.
19 citations
TL;DR: In this article, active carbons were prepared by activating carbonized products (obtained by pyrolysis of olive wood in nitrogen at 1073 K) and olive wood itself under a flow of carbon dioxide at 1048 K.
Abstract: Active carbons were prepared by activating carbonized products (obtained by pyrolysis of olive wood in nitrogen at 1073 K) and olive wood itself under a flow of carbon dioxide at 1048 K. The effect on the development of surface area and porosity of such variables as activation time, heating rate, previous carbonization time, and starting material (either carbonized samples or wood) were followed by adsorption of nitrogen at 77 K. Changes of meso- and macroporosity during the activation process were monitored by mercury porosimetry. Surface area (BET values) varies from 469 up to 854 m2.g–1. A development of micro, meso and macroporosity takes place depending on activation time.
19 citations
TL;DR: Results show that both in situ and in vivo the glutathione reductase of Escherichia coli is subjected to a redox interconversion mechanism probably controlled by the intracellular NADPH and GSSG concentrations.
Abstract: The redox interconversion of Escherichia coli glutathione reductase has been studied both in situ, with permeabilized cells treated with different reductants, and in vivo, with intact cells incubated with compounds known to alter their intracellular redox state.
17 citations
TL;DR: The anatomy of the human aortic valve was studied by SEM in 36 subjects without cardiac pathology who had died of various accidental causes, suggesting that fenestrations appear initially as small perforations which then coalesce to form larger apertures.
Abstract: The anatomy of the human aortic valve was studied by SEM in 36 subjects without cardiac pathology who had died of various accidental causes. Villous and lamellar tissue excrescences were observed at the node of Arantius and at the limit between the lunules and the load-bearing portion of the leaflets. The morphology of these structures suggests that they represent areas in which valve tissue becomes detached into the bloodstream. Fenestrations were present in the lunules of 14 specimens, with a higher incidence in specimens from subjects who were middle-aged or older. Our observations suggest that fenestrations appear initially as small perforations which then coalesce to form larger apertures. Two main types of endothelial cells, elongated and polygonal were detected on the endothelial surface of the leaflets. Both types of cells display a constant mode of arrangement on the different segments of the leaflets (lunules, node of Arantius and load-bearing portion of the leaflet). The possible relationships between endothelial cell morphology and the pattern of mechanical stress to which the leaflets are subjected is discussed.
17 citations
TL;DR: In this article, the reaction of 2-amino-2-deoxy-d - glycero -d - altro-heptose hydrochloride with acyclic and cyclic 1,3-dicarbonyl compounds gives, respectively, ( d - allo -pentitol-1-yl)-pyrroles and -tetrahydroindoles that can be dehydrated to yield d - ribo - C -glycosyl heterocycles having furanoid or pyranoid structures, depending on
14 citations
TL;DR: It is suggested that lipid dilution of protein in these reconstituted systems induce a decrease of the level of self-quenching by promoting dissociation of (Ca2+, Mg2+)-ATPase.
TL;DR: In this article, a new fluorometric method for the determination of lithium based on the formation of a fluorescent species with 1,4-dihydroxyanthraquinone (Quinizarine), in acetone-water (90-10%) medium and 10−3M in NaOH is described.
TL;DR: A selective and sensitive method is described for the determination of trace amounts of molybdenum, based on its reaction with thiocyanate and its extraction (into toluene) as an ion-association complex formed with adogen.
TL;DR: In this article, the reactivity of isophthaldihydroxamic acid against inorganic ions is established and a spectrophotometric study of its reaction with Mn(II) shows that a complex of stoichiometry 1:2 (Mn:L) is formed.
TL;DR: In this article, 1,3-Cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride produces colored solutions with iodate ions in acid medium and the yellow color obtained has been used to proposed Spectrophotometric methods for determination of IO 3 − in the concentration range 1.0-11.0 ppm in acetic acid medium.
TL;DR: The above findings suggest the occurrence of cytosolic and particulate degradative pathways for dinucleoside polyphosphates in rat liver supernatant and precipitate respectively.
TL;DR: In dogs fitted with a pancreatic cannula and a duodenal cannula the intake of a standard meal induced a significant increase in the flow of pancreatic secretion and in the output of amylase, total protein, bicarbonate and chloride and the implications of secretin, gastrin and cholecystokinin (CCK) on these effects are discussed.
Abstract: In dogs fitted with a pancreatic cannula and a duodenal cannula the intake of a standard meal induced a significant increase in the flow of pancreatic secretion and in the output of amylase, total protein, bicarbonate and chloride. The oral administration (200 mg/day) of cimetidine to dogs was seen to elicit a marked decrease in postprandial flow increase and bicarbonate output, coinciding with a significant increase in amylase and total protein output. At the same time the postprandial duodenal pH remained at levels similar to those obtained in basal periods. The implications of secretin, gastrin and cholecystokinin (CCK) on these effects are discussed.
TL;DR: Determination of Magnesium by Spectrofluorimetry and Synchronous Scanning First and Second Derivative SpectroFLimetry with 2-Quinizarinsulpbonate.
Abstract: Determination of Magnesium by Spectrofluorimetry and Synchronous Scanning First and Second Derivative Spectrofluorimetry with 2-Quinizarinsulpbonate
TL;DR: Yeast 1,3-beta-D-glucan synthetase (EC 2.4.1.34) activity is modulated by endogenous factors obtained by the extraction of different subcellular fractions with hot water, which results in activation by the stimulatory material and the combined effect of GTP and activating material derived from cell wall fractions was supraadditive.
TL;DR: IMP dehydrogenase (EC 1.2.14) has been purified near homogeneity from Artemia embryos and can occur in a number of oligomeric forms depending on the ionic strength of the medium.
Abstract: 1. 1. IMP dehydrogenase (EC 1.2.1.14) has been purified near homogeneity from Artemia embryos. 2. 2. The K m values for IMP and NAD + were 15 and 200 μM, respectively. 3. 3. GMP, XMP, GTP, guanosine 5′-tetraphosphate and diguanosine tetraphosphate (Gp 4 G) were competitive inhibitors of the reaction towards IMP with K i values of 140, 180, 175, 120 and 87 μM, respectively. 4. 4. The enzyme from the 27,000 g supernatant can occur in a number of oligomeric forms (450, 375, 260 or 220 kDa) depending on the ionic strength of the medium. 5. 5. Upon precipitation with ammonium sulphate (0.3–0.4 saturation) the enzyme aggregates forming complexes of more than 1000 kDa.
TL;DR: In this article, the basis set superposition effects may arise in Ab Initio calculations of electronic properties of the hydrogen-bonded systems, and the counterpoise technique of Boys and Bernardi in conjunction with the charge descomposition method of Morokuma is employed in order to examine the dependence of the components of the basis-set superposition error.
Abstract: Basis set superposition effects, which may arise in Ab Initio calculations of electronic properties of the hydrogen bonded systems, are analized. The counterpoise technique of Boys and Bernardi in conjunction with the charge descomposition method of Morokuma is employed in order to examine the dependence of the components of the basis set superposition error. Prototype calculations for the HNOH 2 O system are presented.
TL;DR: Isophthaldihydroxamic acid produces colored solutions with molybdate ions in basic medium and the resultant product is extracted into a toluenic solution of trioctylmethylammonium chloride (Adogen) as mentioned in this paper.
TL;DR: Long-time runs of molecular-dynamics computer simulations of a two-dimensional Lennard-Jones system without any scaling procedure show spontaneous fluctuations except when the system is far from the melting zone.
Abstract: We have performed long-time runs of molecular-dynamics computer simulations of a two-dimensional Lennard-Jones system, without any scaling procedure. The thermodynamic properties show spontaneous fluctuations except when the system is far from the melting zone.
TL;DR: In this article, a spectrophotometric method of Cr(VI) determination in the concentration range 0.40-9.5μg ml−1 (e=5600 mole−1-cm−1 at 485 nm) was proposed.
Abstract: 2-Oximinodimedone dithiosemicarbazone reacts with Cr(VI) in strongly acid medium. The orange colour obtained has been used to propose a spectrophotometric method of Cr(VI) determination in the concentration range 0.40–9.5μg ml−1 (e=5600 mole−1-cm−1 at 485 nm). The stoichiometry of the reaction is 3∶2 (reagent∶Cr(VI)) which is in accordance with the oxidation reaction of the reagent by Cr(VI). The method has been applied to the determination of Cr(VI) and Fe(III) in ceramic materials.
TL;DR: In this article, the yellow color obtained has been used to propose a spectrophotometric method of C10 3 − determination in the concentration range 0.5 − 6.0 ppm (molar absorptivity 1.26 × 10 4 liters mol −1 cm −1 at a wavelength of 397 nm).
TL;DR: The reaction of aldoses with an excess of amine and hydrogen cyanide can yield a series of cyclic and acyclic compounds in addition to the expected α-aminoaldonononitriles.
TL;DR: In this paper, a direct spectrophotometric method is proposed to determine Mg(II) based on the extraction in isoamyl alcohol of the complex formed between Mg (II) and 1,8-dihydroxyanthraquinone.
TL;DR: The properties and analytical possibilities of 1,3-cyclohexanedione bis(4-methylthiosemicarbazone) monohydrochloride as spectrophotometric reagent have been examined.
TL;DR: In this article, the catalytic effect of copper(II) on the atmospheric oxidation of 1,3-cyclopentanedione bis(4-methylthiosemicarbazone) monohydrochloride was investigated.