Showing papers by "University of Seville published in 1982"

Numerical Taxonomy of Moderately Halophilic Gram-negative Rods

Abstract: Summary: A study was made of 516 randomly selected isolates of moderately halophilic bacteria from solar salterns showing salinities between 8.8 and 40.0% (w/v) total salts, located in S.E. Spain. After purification, many cytological, physiological, biochemical, nutritional and antibiotic sensitivity characters were determined for 106 selected saltern isolates and two reference strains. Data were coded and analysed by numerical techniques using the Jaccard coefficient (S j), and clusters of strains were obtained by average linkage (UPGMA) analysis. Nine major phenons were found at the 72.5% similarity level. The properties of each phenon are given, their taxonomic affinities are discussed, and typical reference strains are suggested. Almost all the strains were related to genera known to contain marine species. A large number of the strains could be tentatively assigned to the genus Vibrio, suggesting that this may be an abundant taxon of moderately halophilic Gram-negative rods in solar salterns.

Genes involved in the control of nuclear fusion during the sexual cycle of Saccharomyces cerevisiae.

Abstract: Mutants of Saccharomyces cerevisiae defective for nuclear fusion have been isolated. Their mutations have been characterized by meiotic analysis, dominance-recessivity and complementation. Twelve of the mutations are allelic to the previously described kar 1−1; five affect a second gene designated KAR 2 and three affect a third gene designated KAR 3. There is evidence suggesting that other two mutants are affected in a gene different from the three mentioned.

Regulation of the nitrate-reducing system enzymes in wild-type and mutant strains of Chlamydomonas reinhardii

Abstract: Six mutant strains (301, 102, 203, 104, 305, and 307) affected in their nitrate assimilation capability and their corresponding parental wild-type strains (6145c and 21gr) from Chlamydomonas reinhardii have been studied on different nitrogen sources with respect to NAD(P)H-nitrate reductase and its associated activities (NAD(P)H-cytochrome c reductase and reduced benzyl viologen-nitrate reductase) and to nitrite reductase activity. The mutant strains lack NAD(P)H-nitrate reductase activity in all the nitrogen sources. Mutants 301, 102, 104, and 307 have only NAD(P)H-cytochrome c reductase activity whereas mutant 305 solely has reduced benzyl viologen-nitrate reductase activity. Both activities are repressible by ammonia but, in contrast to the nitrate reductase complex of wild-type strains, require neither nitrate nor nitrite for their induction. Moreover, the enzyme from mutant 305 is always obtained in active form whereas nitrate reductase from wild-types needs to be reactivated previously with ferricyanide to be fully detected. Wild-type strains and mutants 301, 102, 104, and 307, when properly induced, exhibit an NAD(P)H-cytochrome c reductase distinguishable electrophoretically from contitutive diaphorases as a rapidly migrating band. Nitrite reductase from wild-type and mutant strains is also repressible by ammonia and does not require nitrate or nitrite for its synthesis. These facts are explained in terms of a regulation of nitrate reductase synthesis by the enzyme itself.

Point defects and high-temperature creep of non-stoichiometric NaCl-type oxide single crystals I. NiO

Abstract: Creep of NiO single crystals has been investigated by compression along 〈100〉 in the temperature range 0·6T m to 0·8T m, for stresses from 25 to 120 MPa and oxygen partial pressures pO2 from 10−5 to 0·2 atm. The data are analysed using the equation for recovery-controlled creep. The stress exponent decreases from a value of 12 to low temperature to 7 at high temperature; the activation energy is in the range 5·4 to 8·5 eV and the pO2 exponent varies from 0 to -0·17. The rate-controlling mechanism exhibits a change at, about 0·7T m which can be interpreted in two different ways. Oxygen diffusion plays a dominant role in the rate-controlling mechanism of creep, and occurs via a vacancy mechanism.

Genetics of carotene biosynthesis in Phycomyces.

Abstract: Genetic analysis of carotenogenesis in Phycomyces is hampered by the inability of most mutants to complete the sexual cycle. Heterokaryons between complementing mutants or between a mutant and a helper strain are, however, fertile. Using this method crosses have been carried out between mutants representing the different known genes and phenotypes. The gene for phytoene dehydrogenase, carB, is closely linked to carRA, a bifunctional gene specifying both lycopene cyclase and a product involved in substrate transfer. The regulatory gene carS lies on the same chromosome, but not close to the structural genes. The situation is thus reminiscent of an operon. Two chemoinsensitive mutants, showing little or no response to the effects of retinol and 2-(4-chlorophenyl)thiotriethylamine HCl on carotenogenesis, carry mutations in separate genes. One of these is probably identical with carRA; the other is a new gene termed carl.

Photoinactivation of spinach nitrate reductase sensitized by flavin mononucleotide. evidence for the involvement of singlet oxygen

Abstract: All the activities of the nitrate reductase complex from spinach are irreversibly inactivated by irradiation of the enzyme with blue light in the presence of flavin mononucleotide. The photoinactivation requires oxygen and is prevented by ethylenediaminetetraacetic acid and by reduced nicotinamide adenine dinucleotide, but not by superoxide dismutase plus catalase. On the other hand, the inactivation is markedly enhanced in 77% deuterated water and it is suppressed by the singlet oxygen quenchers azide, histidine and tryptophan. All these results suggest that singlet oxygen generated by light absorption by flavin mononucleotide, rather than excited flavin mononucleotide or other oxygen species, is the primary agent involved in the photooxidative inactivation of the enzyme.

Photosynthetic production of ammonia

Abstract: The conversion of solar energy into suitable redox energy through photosynthesis of the water-splitting type carried out by intact or reconstituted systems is of great interest and significance, and a major effort is presently under way to use this process to provide ‘biofuels’ on a renewable basis The fact that some photosynthetically generated metabolites are highly reduced compounds of immediate practical interest has, however, been overlooked until now Such is the case of ammonia, a compound generated by green cells from oxidized inorganic nitrogenous substrates in light-driven reactions, and that, in itself, is a very valuable derivative, both as a fuel and as a fertilizer1,2

Kinetics of desorption from a heterogeneous surface

Abstract: Mathematical equations governing kinetics of desorption from heterogeneous surfaces are derived from a master equation with the assumption that only nearest-neighbor adatoms interact. A number of cases are analyzed: random, periodical, and patchwise distributions of sites characterized by different activation energies. In general, the kinetic equations obtained must be solved numerically. We have performed numerical calculations for several specific cases and analyzed the influence exerted by heterogeneity and lateral interaction between adatoms on the desorption rate $\frac{d\ensuremath{\bigominus}}{\mathrm{dT}}$. The results obtained make it clear that, due to lateral interaction, the desorption curves are very sensitive to the way in which heterogeneities are distributed on the surface (periodically, patches with different sizes, etc.).

Influence of the Co2 pressure on the kinetics of thermal decomposition of manganese carbonate

Abstract: Kinetic analysis has been performed on TG and DTG diagrams of the forward reaction MnCO3⇌ MnO + CO2, recorded at different pressures of CO2 ranging form 2.6. 10−4 Pa to 26.6 kPa. The results obtained show that this reaction follows a first-order kinetic law, independently of the CO2 pressure used in carrying out the experiments. On the other hand, the activation energy increases on increase of the CO2 pressure, from 117 kJ/mol up to an asymptotic value of 292 kJ/mol at about 26.6 Pa. This finding cannot be explained by considering the influence of the reverse reaction of formation of MnCO3, for under the described experimental conditions the ratio\(P_{CO_2 } /P_{equil} \) to zero. A mechanism that takes into account the adsorption of CO2 on the phase boundary has been proposed in order to interpret the results.

Histochemical and ultrastructural studies on the salivary glands of Helix aspersa (Mollusca)

Abstract: A histochemical and ultrastructural study was carried out on the salivary glands of adult specimens of Helix aspersa. Histochemically four cell types were distinguished: mucocyte I, mucocyte II, pseudochromosome cell and protein cell. The first secretes neutral and acid mucins. Mucocyte II and pseudochromosome cells produce acid mucins and the protein cell secretes neutral mucins and proteins. The ultrastructural data for differentiating these four cell types is discussed. Mucocytes I have a characteristic arrangement of rough endoplasmatic reticulum and basal infoldings. Mucocytes II have pseudocrystalline formations in the rough endoplasmatic reticulum and intraluminary ducts. Pseudochromosome cells have typical granules with a reticular central zone. Protein cells have serous homogenous secretion. The epithelium of the salivary ducts is described.

Optimization of Conditions for Photoproduction of Ammonia from Nitrate by Anacystis nidulans.

Abstract: The effect of several relevant environmental factors influencing the photoproduction of ammonia from nitrate by Anacystis nidulans cells treated with the glutamine synthetase inhibitor l-methionine-dl-sulfoximine has been investigated. The optimal ratio between l-methionine-dl-sulfoximine concentration (micro-molar) and cell density (micrograms of chlorophyll per milliliter) was around 1, the process taking place at maximal rate at a temperature of about 40°C, within the pH range of 7 to 10. Ammonia production was stimulated by CO2 or bicarbonate and was not affected by the accumulation of ammonia in the medium up to concentrations of 30 mM. The rate of ammonia production was found to be determined by the interaction of at least four factors, namely, irradiance and the density, depth, and turbulence of the cell suspension. Ammonia photoproduction from nitrate and water represents an interesting process for the conversion of light energy into chemical energy, which can operate at high efficiency, around 30% of its theoretical maximum.

Characterization of oxide Co-Mo/γ-Al2O3 hydrodesulphurization catalysts prepared by different methods

Abstract: Three series of oxidic Co-Mo/γ-Al2O3 catalysts with different cobalt content and prepared by three different methods have been studied by X-ray diffraction, diffuse reflectance spectroscopy and magnetic techniques. The results show that the formation of Co and Mo surface species is affected by the method of catalyst preparation and that Mo enhances the dispersion of the cobalt species. The presence of Co3 O4 was clearly detected in cobalt-rich samples prepared by a two-step method, especially when Mo was incorporated by equilibrium adsorption. It also seems that in catalysts prepared by “wet” consecutive impregnation Co favours the formation of a Mo multilayer on the surface of Al2O3. However, in catalysts prepared by simultaneous impregnation the segregation of Co3O4 and the formation of a Mo multilayer occurs less extensively.

Indole acetic acid production by Rhizobium: Effect of 2-ketoglutaric acid

Abstract: I ndole acetic acid (IAA) production from tryptophan by cell suspensions of Rhizobium trifolii, R. leguminosarum, R. phaseoli and R. lupini was studied in the presence or in the absence of 2-ketoglutaric acid. In R. lupini, production of IAA was strongly enhanced by the ketoacid, but in fast growing rhizobia it was less enhanced or unaffected. On the other hand, glutamic acid inhibits IAA production by R. meliloti, but stimulates IAA production in both R. leguminosarum and R. phaseoli. A hypothesis is proposed to explain these results.

Sustained photoproduction of ammonia from nitrate by Anacystis nidulans

Abstract: Conditions that lengthen the time during which l-methionine-dl-sulfoximine (MSX) promotes excretion of ammonia produced by photosynthetic nitrate reduction in Anacystis nidulans have been sought. If MSX was added every 24 h, maximal rates of ammonia production were maintained for 3 days. After this time, ammonia production ceased due to a specific deficiency of glutamine in the cells, which finally led to cell lysis. The effective ammonia production period could be further extended either by adding a low amount of glutamine at the end of the 3-day period or by allowing the cells to recover for 8 h in the absence of MSX after every 48-h period in the presence of inhibitor. In this way, a steady production of ammonia lasting for at least 10 days was achieved. The MSX-treated cyanobacterial cells thus represent a system relatively stable with time for the conversion of light energy into chemical energy through the photoreduction of nitrate to ammonia.

Implicaciones educativas de los estilos cognitivos

Abstract: RESUMENSe plantea el problema de la adecuacion de los contenidos y las tecnicas educativas a los estilos cognitivos del alumno. Muchas investigaciones han mostrado la relacion entre reflexividad-impulsividad y rendimiento escolar. Nuestro sistema educativo actual parece favorecer las habilidades propias de los sujetos reflexivos. En este sentido, muchos trabajos han investigado los procedimientos para modificar el estilo cognitivo hacia la reflexividad, ya que este estilo se considera mas adaptativo. En relacion al estilo cognitivo dependencia-independencia de campo (DIC) se han encontrado diferencias en el aprendizaje segun los contenidos, el tipo de reforzamiento, las diferentes formas de motivacion (extrinseca o intrinseca) y los “mediadores del aprendizaje” utilizados. Se plantea la necesidad de adaptar los contenidos y los procedimientos a las necesidades de los distintos alumnos, y la de encontrar la manera de ayudarlos a diversificar sus estrategias de aprendizaje.

Upper and lower bounds on capacitances of coupled microstrip lines with anisotropic substrates

Abstract: The Fourier transform has been used to obtain stationary expressions for the even- and odd-mode capacitances of coupled microstrip lines on anisotropic substrates. Expressions for calculating the upper and lower bounds on true values have been found using variational techniques; so the margins of error in the calculation can be estimated. The method is used to compute the even- and odd-mode characteristics of coupled microstrip lines on sapphire, and to study the effect of substrate anisotropy on the line characteristics.

Dissociation of FAD from the NAD(P)H-Nitrate Reductase Complex from Ankistrodesmus braunii and Role of Flavin in Catalysis

Abstract: Ankistrodesmus braunii NAD(P)H-nitrate reductase is a complex hemoflavomolybdoprotein composed by eight similar subunits. The flavin prosthetic group, identified as FAD, is essential for the NAD(P)H-dependent activities of the complex, and is located before the heme chromo- phore in the enzyme electron transport chain from reduced pyridine nucleotides to nitrate. Fluorescence studies indicate that nitrate reductase can dissociate about 80% of its FAD by incubation at room temperature, the flavin dissociation being followed by a parallel decrease of NADH-nitrate reductase activity. Dissociation of FAD from the protein is easily increased by dilution or prolonged dialysis of the enzyme preparations. However, exogenous FAD specifically prevents the dissociation of enzyme-bound flavin, and protects the NAD(P)H-dependent activities. The Km for FAD, as a protector of NADH-cytochrome c reductase activity, is 4 nᴍ. In addition, dithioerythritol also prevents the flavin dissociation, and therefore the presence of free sulphydryl groups in the FAD-domain is suggested. FAD-depleted nitrate reductase, obtained by several methods, is unable to recover its original activity when incubated in the presence of FAD alone or with thiols.

Electron microscopy study of crystallization behaviour of Fe40Ni38Mo4B18 (2826 MB) metallic glass

Abstract: Crystallization behaviour of 2826 MB metglas has been studied by transmission electron microscopy and selected area diffraction. Dynamic heating between room temperature and 1100 K and isothermal annealing close to crystallization onset have been performed. Crystallization takes place through a two-stage process to give MSI and MSII phases and details of these are discussed. A new transformation to a stable phase SIII is detected in agreement with the third peak observed by differential thermal analysis experiments.

Los estilos cognitivos. Introducción al problema de las diferencias cognitivas individuales

Abstract: RESUMENAdemas de la busqueda de unos principios generales, una de las preocupaciones de la Psicologia Cognitiva ha sido la forma en que esas leyes se encarnan en el funcionamiento de los individuos concretos. Estas diferencias individuales en la cognicion son conocidas como “estilos cognitivos”. Muchos autores desde distintas perspectivas se han preocupado por el estudio de este tema, aunque el enfoque predominante hoy en dia es el estudio de las diferencias individuales en lo relativo a las estrategias en la resolucion de problemas. Se han propuesto varios tipos de estilos cognitivos, pero los dos estilos conocidos como “reflexibilidad-impulsividad” y la “dependencia-independencia de campo” son los mas investigados y los que poseen mas implicaciones educativas.

Benign cutaneous cystic teratoma.

Abstract: Cutaneous teratomas, arising from 3 germinal layers, are extremely rare and must be distinguished from dermoid cysts and other dysembryoplasias. An exceptional case of cutaneous cystic teratoma is described in which respiratory epithelium and thyroid, muscle and nervous tissues were noteworthy features. After discussing the differential diagnosis, and based on the presence of multiple cystic cavities, well-differentiated tissues, the congenital onset, the localization and evolution, it is concluded that the tumor was benign in nature.

Crystallization kinetics of Fe40Ni38Mo4B18 and Fe80B20 metallic glasses

Abstract: Experimental results for magnetic susceptibility, calorimetry and electrical resistivity for the metallic glasses 2826 MB (Fe40Ni38Mo4Bi18) and 2605 (Fe80B20) are reported. The crystallization kinetics of these alloys is investigated and activation energies are estimated. Time variation of crystallized fraction derived from isothermal electrical runs is interpreted to give the preponderant mechanisms involved in the crystallization process.

Benzyl viologen-mediated in vivo and in vitro inactivation of glutamine synthetase in Azotobacter chroococcum.

Abstract: Addition of benzyl viologen to a cell suspension of the aerobic bacterium Azotobacter chroococcum growing on nitrate resulted in a rapid loss of glutamine synthetase activity as assayed in situ. When a glutamine synthetase preparation which exhibited NADH-benzyl viologen oxidoreductase activity was incubated, under air, with NADH and benzyl viologen, glutamine synthetase was inactivated in a short period of time. This in-vitro inactivation process could be prevented in the presence of added catalase, thus indicating that hydrogen peroxide was involved in the process, and by EDTA, suggesting that metal ions are also involved. The characteristics of the benzyl viologen-dependent glutamine synthetase inactivation observed with externally added H2O2 and a preincubated sample are similar. Inhibition of glutamine synthetase inactivation by histidine suggests that hydroxyl radicals, or something with similar reactivity, is the inactivating agent. The fact that inactivation can also be catalyzed by a model system consisting of Fe2+ and H2O2 leads to the conclusion that hydroxyl radicals are most likely produced in a Fenton reaction in which hydrogen peroxide reacts with adventitious iron ions. Since A. chroococcum contained a high level of catalase it may be concluded that cellular compartmentation plays an important role in the in-vivo inactivation of glutamine synthetase.

Suppression of the normal autologous mixed leukocyte reaction by sera from patients with systemic lupus erythematosus

Abstract: Sera from 15 patients with active systemic lupus erythematosus and 7 patients with inactive lupus were added to normal autologous mixed leukocyte reaction (MLR) cultures. Twelve of the 22 sera reduced autologous T cell proliferative responsiveness to B plus null (B + N) cells or macrophages by 50% or more. This inhibition correlated with defective autologous MLR in fresh mononuclear cells from those patients. When normal responding and stimulating cell populations were preincubated with suppressive lupus sera, then added to autologous MLR cultures that contained normal serum, proliferative responses were also reduced; inhibitors are directed against participating mononuclear cell subpopulations. The suppressive serum factors were directed variously against monocyte/macrophage (M phi), B + N, or T cell populations; M phi/T interactions were suppressed most frequently. The inhibitors were not removed by high-speed centrifugation or by depletion of antibodies to DNA, and they did not correlate with the presence of lymphocytotoxic antibodies. The presence of serum inhibitors of normal M phi/T and B + N/T autologous MLR may be an immunologic abnormality important in the initiation, perpetuation, or exacerbation of systemic lupus erythematosus.