Screening for and characterization of phospholipase A1 hypersecretory mutants of Tetrahymena thermophila Hartmann, M.; Guberman, Alejandra Sonia; Florin-Christensen, M.; Tiedtke, A. We have described a procedure for the isolation of mutants of Tetrahymena thermophila with hyperscretion of phospholipase A1 (PLA1). Using random chemical mutagenesis, uniparental cytogamy, genetic crossing and a new, fast and effective screening procedure, four PLA1-hypersecretory mutants were isolated. The screening procedure is based on the formation of a halo appearing around cylindrical holes in a lecithin-containing agar plate filled with cell-free supernatants. About 3,940 clones were tested with this procedure in primary screening for hypersecretory features, of which 60 putative hypersecretory mutants were isolated, subcloned and tested in a secondary screening. Of these, four selected mutants showed 1.8-2.2 more PLA1 activity in the cell-free supernatants compared to the wild-type strain CU 438.1. Hypersecretion was only observable for PLA1; no increased activity for two other lysosomal enzymes could be detected. These hypersecretory mutants of T. thermophila can be very useful for increasing the yield of PLA1 in fermentation processes. This is particularly relevant because, in contrast to other phospholipases, PLA1 is not available on the commercial market for fine chemicals and little is known about the role of PLA1 in cell signaling and metabolism.

Relaciones fronterizas en la Cordillera Chubutense: Actividades productivas y circuitos de comercialización (1900-1920) Gavirati, Jorge Marcelo; Finkelstein, Débora; Novella, María Marta En este trabajo se obtienen explicaciones relacionadas con los antecedentes y conformación de las unidades económicas minifundistas –cuyos titulares eran en su mayoría migrantes chilenos– de una sección catastral del noroeste del Territorio Nacional del Chubut, en el período 1900-1920. A partir del análisis de datos referidos a las mismas, se describen las características productivas y los circuitos de comercialización en los que participaban los bienes producidos. Estos circuitos tienen antecedentes en las prácticas aborígenes y, a comienzos del período considerado, se volcaban mayoritariamente hacia los mercados chilenos. Estas prácticas comerciales deben vincularse con la procedencia de los productores, las relaciones establecidas con los centros de intercambio ubicados en Neuquén –región por la que muchos de ellos habían realizado su ingreso al país y residido durante algún tiempo–, la transitabilidad de los pasos cordilleranos utilizados y la inexistencia de trabas aduaneras. Por otra parte, era la práctica comercial implementada también por la unidad económica latifundista más importante de la región. Los pobladores, provenientes del Oeste no percibían en una primera etapa las posibilidades de comerciar con el área atlántica con la que no se encontraban relacionados. No obstante, se perfilaban ya algunas problemáticas que irían paulatinamente inclinando los flujos comerciales hacia ese sector. Entre otras, la presencia más notoria del Estado argentino y de sus representantes en el territorio, la implementación de distinto tipo de restricciones aduaneras por parte de los dos estados, el trazado de caminos y líneas y vías férreas que vinculan la zona cordillerana con la costa atlántica, y la presencia a partir de la década del 20 de flujos poblacionales provenientes de ese sector y con relaciones comerciales con él.

Nutritional requirements and nitrogen-dependent regulation of proteinase activity of Lactobacillus helveticus CRL 1062 Hebert, Elvira Maria; Raya, Raul Ricardo; Savoy, Graciela The nutritional requirements of Lactobacillus helveticus CRL 1062 were determined with a simplified chemically defined medium (SCDM) and compared with those of L. helveticus CRL 974 (ATCC 15009). Both strains were found to be prototrophic for alanine, glycine, asparagine, glutamine, and cysteine. In addition, CRL 1062 also showed prototrophy for lysine and serine. The microorganisms also required riboflavin, calcium pantothenate, pyridoxal, nicotinic acid, and uracil for growth in liquid SCDM. The growth rate and the synthesis of their cell membrane-bound serine proteinases, but not of their intracellular leucyl-aminopeptidases, were influenced by the peptide content of the medium. The highest proteinase levels were found during cell growth in basal SCDM, while the synthesis of this enzyme was inhibited in SCDM supplemented with Casitone, Casamino Acids, or β-casein. Low-molecular-mass peptides (<3,000 Da), extracted from Casitone, and the dipeptide leucylproline (final concentration, 5 mM) play important roles in the medium-dependent regulation of proteinase activity. The addition of the dipeptide leucylproline (5 mM) to SCDM reduced proteinase activity by 25%.

Acid-base properties and active site requirements for elimination reactions on alkali-promoted MgO catalysts Diez, Veronica Karina; Apesteguia, Carlos Rodolfo; Di Cosimo, Juana Isabel Base-catalyzed elimination reactions were studied on MgO and alkali-modified MgO catalysts using 2-propanol as a probe reactant. The effect of the acid–base properties on the catalyst activity and selectivity was investigated by modifying the surface properties of MgO with 1 mol% of alkaline metals. Group IA metals promote the formation of medium- and high-strength basic sites, thereby increasing the basic site density and strength. The addition of alkaline promoters improves the MgO activity for 2-propanol conversion reactions. The selectivity toward dehydration or dehydrogenation products depends on the base site nature, so that intermediate-strength base sites promote acetone formation, whereas high-strength base sites selectively yield propylene. 2-Ppropanol decomposition to acetone and propylene is proposed to take place via an E1cB mechanism in two parallel pathways sharing a common 2-propoxy intermediate.

An inquiry into the nature of the gamma-ray source 3EG J1828+0142 Punsly, Brian; Romero, Gustavo Esteban; Torres, Diego F.; Combi, Jorge Ariel The unidentified, low-latitude, gamma -ray source 3EG J1828+0142 presents high levels of variability and a steep spectral index Gamma ~ 2.7. Here we propose a model for this source where the high-energy emission is produced by a galactic Kerr-Newman black hole. The model takes into account electron-positron annihilation losses in the calculation of the expected spectral energy distribution and can reproduce the observational features, including the absence of a strong radio counterpart. We also report the discovery of a nearby supernova remnant that could be associated with the original supernova explosion that created the black hole. Several faint radio sources were also detected in the radio field within the inner gamma -ray confidence contour and their spectral index estimated. Some of these sources could be the expected weak radio counterpart.

Geomorfología de estuarios: una visión diferente Piccolo, Maria Cintia; Perillo, Gerardo Miguel E. Los estuarios son una de las mas importantes caracteristicas de las zonas costeras sujetas a fuertes procesos de interaccion mar-continente en un amplio rango de escalas espacio-temporales. En general, estos ambientes ocupan las areas costeras menos expuestas ala accion marina, permitiendo el desarrollo de puertos, facilidades recreacionales 0 apropiados emprendimientos de acuicultura, Sin embargo, dentro de los estuarios los procesos dinamicos son significativos imponiendo un marc ado stress sobrela biota, ya sea pennanente 0 temporaria, la morfologia y las construccione.

Integración, fronteras y movilidad espacial de la población Meichtry, Norma Cristina Se analizan los posibles argumentos que pudieran respaldar los procesos de cambios que se vienen registrando en la frontera entre Argentina y Paraguay, desde el punto de vista de la teoría de la nueva división del trabajo en el marco de un sistema mundial o de la teoría de la generalización de las crisis socioeconnómicas a partir de los procesos de reestructuración de la economía.

Análisis empírico de algoritmos de inversión de matrices, aplicados al cálculo de propiedades moleculares. Godoy, María Viviana; Provasi, Patricio Federico; Aucar, Gustavo Adolfo En este articulo se evahia la performance en cuanto a tiempos de ejecuci6n de dos algoritmos de inversi6n de matrices: uno tradicionalmente utilizado en calculos de propiedades moleculares y uno nuevo implementado en nuestro grupo de investigaci6n y que utiliza un desarrollo en sene de potencias de los elementos matriciales. Se probaron distintas plataformas, sistemas operativos, compiladores y subrutinas de algebra lineal (BLAS). Se realizaron calculos para compuestos modelo que requieren el tratamiento de matrices conteniendo entre 80.000 y 4.000.000 de elementos. Se obtuvieron los tiempos de ejecuci6n de dichos algoritmos a traves de la evaluaci6n con el metodo de propagadores de polarizaci6n de propiedades moleculares tipo triplete y singulete. Se observ6 que el rendimiento del algoritmo de la serie aumenta al crecer la dimensi6n de la matriz a invertir. Para todas las plataformas utilizadas se obtuvo una performance ganancioso de la serie con respecto al algoritmo tradicional.; In this article, the performance of two algorithms for matrix inversion are evaluated considering as a parameter the times of execution: one traditionally used in the calculations of molecular properties and a new one implemented in our research group, that makes use of a series development of matrix elements. Different platforms, operating sistems, compilers and subroutines of lineal algebra (BLAS) were investigated. Calculations for model compounds that require the treatment of matrix containing a number of elements between 80.000 and 4.000.000 was carried out. The calculation of molecular properties of both, singlet and triplet type was used to evaluate the execution time of these algorithms. It was observed that the performance of the series algorithm increases when the dimension of the given matrix grows. For all plataforms, a gainful performance of the series was obtained, compared to the tradicional algorithm.

Transmetallations between aryltrialkyltins and borane: Synthesis of arylboronic acids and organotin hydrides Faraoni, María Belén; Koll, Liliana Cristina; Mandolesi, Sandra Delia; Zuñiga, Adriana Elena; Podestá, Julio Cesar Aryltrialkyltin compounds react with borane in THF to give mixtures of trialkyltin hydrides and arylboranes, which on hydrolysis give arylboronic acid in high yields. The arylboronic acids are easily separated and obtained free of organotins.

Desarrollo de un modelo de ahorro de energía en edificios de vivienda y determinación de valores límite de calidad térmica para la República Argentina Czajkowski, Jorge Daniel La definición de valores admisibles de uso normativo es de características especiales ya que poseen un cierto grado de arbitrariedad. Esto depende de muchos factores entre los que podemos mencionar los de carácter técnico, científico, práctico y político. La definición de estándares se complejiza por la variabilidad climática y la necesidad de compatibilizar modelos y procedimientos desarrollados para diferentes escalas de aplicación. Se presenta el modelo desarrollado, se discute sobre las dificultades encontradas en la determinación de los valores admisibles para los diversos climas de la Argentina y se comentan las resistencias para su aplicabilidad como normativa.; The acceptable values definition of normative use is of special characteristics since they have a certain arbitrariness degree. This depends on many factors, technical, scientific, practical and political. The standard definition turns more complex by the climatic variability and the necessity to compatibilize models and procedures developed for different application degrees. The developed model is presented, the difficulties found in the acceptable values determination for the Argentine diverse climates are discussed and the resistances for its applicability as normative is commented.

Chronic stress influences the immune system through the thyroid axis Cremaschi, Graciela Alicia; Gorelik, Gabriela Judith; Klecha, Alicia Juana; Lysionek, Alexis E.; Genaro, Ana Maria The aim of the present work was to analyze the effect of chronic stress on thyroid axis and its influence on the immune response. For this purpose a murine model of chronic stress was developed to evaluate and to correlate thyroid hormone levels with humoral alloimmune response. Results show a reduction in serum levels of thyroid hormones, specially a significant decrease in serum levels of tri-iodotyronine (T3) in stressed animals. On the other hand, alloimmunization was not able to induce an early increment in T3 and thyroxine (T4) levels as it was previously reported in normal animals. In addition, lower titers of alloantibodies were obtained in animals under stress conditions as compared to normal mice. The sustitutive T4 treatment in stressed animals increased significantly alloantibody production as well as the early increment in thyroid hormones after antigenic challenge. These findings suggest that chronic stress induces an alteration of the function of thyroid axis that alters the immune response. (C) 2000 Elsevier Science Inc.

Isobutane/Butene Alkylation:regeneration of solid acid catalysts Querini, Carlos Alberto The regeneration of Y-zeolite catalysts used during the isobutane alkylation reaction is studied. Coke is characterized by temperature-programmed techniques and measuring the H/C ratio. The coke deposited under supercritical conditions is very similar (TPO profile and amount) to the coke deposited in liquid phase. The regeneration was carried out in many ways. Air was used for heating with at a low rate, and holding the temperature at low values for long times. Platinum was incorporated in the zeolite to catalyze the coke combustion or to provide an additional route for coke gasification, such as hydrogenation. Ozone was used to remove most of the coke, followed by a second step with H2 or He. Hydrogen peroxide was studied as an alternative low-temperature oxidation compound. It was found that the ozone treatment, followed by a hydrogen treatment, is an effective way to regenerate this microporous catalyst. The ozone not only eliminates a large fraction of the coke but also changes the characteristics of the small amount of coke left on the catalyst, making it easier to be burnt. The treatment with hydrogen peroxide at 90°C also removes a large fraction of coke, but without changing significantly the characteristics of the coke left after the treatment.

Conversiones religiosas, conversiones seculares: Comparando las estrategias de transformación de identidad en programas de minoridad e iglesias pentecostales Miguez, Daniel Pedro Uno de los problemas que últimamente enfrenta la sociedad argentina es el del crecimiento de su tasa de delincuencia. El delito se ha incrementado en todas sus formas, y dentro de él la delincuencia juvenil no ha sido una excepción. Frente al crecimiento de la delincuencia juvenil, el sistema argentino de minoridad ha implementado una diversidad de políticas, entre las cuales se destaca la de la descentralización de los grandes institutos de menores con regímenes carcelarios cerrados, hacia instituciones más pequeñas, con regímenes abiertos o semi-abiertos. Tal como pasó en los primeros años con la experiencia de Massachussets, las estadísticas muestran que no existen grandes diferencias en los niveles de reincidencia pese al cambio de política. Sin embargo, algunos trabajos estadísticos muestran que las iglesias pentecostales si logran mayores niveles de eficacia, disminuyendo significativamente la reincidencia. El artículo analiza las razones de esta diferencia a partir de la noción de identidad y de ‘organizaciones transformadoras de la identidad’ planteadas por Greil y Rudy.

Economic performance of variable structure control: A case study Figueroa, Jose Luis The operating point of a chemical process is usually computed by optimizing a steady-state objective function, e.g. the profit, subject to the steady-state characteristics of the plant. However, the resulting point typically lies in the boundary of the operating region. The presence of disturbances can easily cause constraint violations in the transient. Thus, it is necessary to move the operating point away from the active constraints into the feasible region. The magnitude of this back-off has a direct influence on the economic side. The purpose of this paper is to study the effect of the combination of a state-observer and controller designed using structure variable techniques at the economical level of the process control.

Potential involvement of C3 complement factor in amphibian fertilization Llanos, Ricardo Javier; Mansilla Whitacre, Cecilia; Miceli, Dora Cristina We have assessed the potential involvement of C3, the third complement factor, and its receptor in Bufo arenarum fertilization. We show that a polyclonal antibody against a B. arenarum C3-like factor (C3Ba) reacts specifically with components of the extracellular matrix (ECM) of coelomic eggs and the cell membrane of uterine eggs. Interestingly, we have identified a 163 kD protein immunoreactive with a monoclonal antibody against the CD11b α chain of the human C3 receptor on the cell membrane of the animal pole of uterine eggs, the site of entry of the sperm, but not in coelomic eggs (CR3Ba). Treatment of coelomic eggs with a pars recta oviductal-like protease, trypsin, induced the translocation of C3Ba from the ECM to the cell membrane. Furthermore, inhibition of CR3Ba by trypan blue, as well as inhibition of C3Ba by anti-C3Ba on uterine eggs impaired fertilization, whereas identical treatment on sperm cells did not alter percentage fertilization. Our results suggest, (A) that changes in the localization of C3Ba from the ECM to the cell membrane may be triggered by trypsin-like proteases during passage of eggs through the oviduct; and (B) that C3Ba/CR3Ba may be involved in B. arenarum fertilization.

Orally administered attenuated Salmonella enteritidis reduces chicken cecal carriage of virulent Salmonella challenge organisms Cerquetti, Maria Cristina; Gherardi, Maria Magdalena Chickens were immunized orally with 109 cfu of the temperature-sensitive (T(s)) mutant E/1/3 of Salmonella enteritidis at 1, 2, 3 and 7 days of age. The animals were challenged with wild-type strains of Salmonella of different serotypes 7 or 14 days following immunization. Chickens receiving multiple oral doses of the vaccine strain showed no signs of disease. Immunized animals shed the vaccine strain for at least 2 weeks after the last inoculation; on the other hand, colonization by the attenuated mutant of internal organs such as spleen and liver was limited. Early exposure of the immunized animals to the virulent bacteria resulted in a reduced cecal colonization by the pathogen. Visceral invasion by the wild-type strain of S. enteritidis or S. gallinarum was drastically diminished in birds challenged 14 days after immunization. Significant differences in the number of these Salmonella were found in the cecal contents, spleen and liver of immunized birds compared with the control animals. In addition, cecal colonization by the virulent strain was reduced in birds challenged with S. typhimurium. These results demonstrate that immunization of newly hatched chickens with live attenuated T(s) mutant E/1/3 of S. enteritidis is safe and reduces Salmonella shedding. (C) 2000 Elsevier Science B.V.

The indirect basal ganglia pathway in dopamine D2 receptor-deficient mice Murer, Mario Gustavo; Dziewczapolski, G.; Salin, P.; Vila, M.; Tseng, Kuei y; Ruberg, M.; Rubinstein, Marcelo; Kelly, M. A.; Grandy, D. K.; Low, M. J.; Hirsch, E.; Raisman Vozari, Rita; Gershanik, Oscar Samuel Recent pathophysiological models of basal ganglia function in Parkinson's disease predict that specific neurochemical changes in the indirect pathway would follow the lack of stimulation of D2 dopamine receptors. Post mortem studies of the basal ganglia in genetically modified mice lacking functional copies of the D2 dopamine receptor gene allowed us to test these predictions. When compared with their congenic N5 wild-type siblings, mice lacking D2 receptors show an increased expression of enkephalin messenger RNA in the striatum, and an increased activity and expression of cytochrome oxidase I in the subthalamic nucleus, as expected. In addition, D2 receptor-deficient mice display a reduced expression of glutamate decarboxylase-67 messenger RNA in the globus pallidus, as the basal ganglia model predicts. This reduction contrasts with the lack of change or increase in glutamate decarboxylase-67 messenger RNA expression found in animals depleted of dopamine after lesions of the mesostriatal dopaminergic system. Furthermore, D2 receptor-deficient mice show a significant decrease in substance P messenger RNA expression in the striatonigral neurons which form the direct pathway. Finally, glutamate decarboxylase-67 messenger RNA expression in the basal ganglia output nuclei was not affected by mutations in the D2 receptor gene, a fact that could probably be related to the absence of a parkinsonian locomotor phenotype in D2 receptor-deficient mice. In summary, these findings provide compelling evidence demonstrating that the lack of endogenous stimulation of D2 receptors is sufficient to produce subthalamic nucleus hyperactivity, as assessed by cytochrome oxidase I histochemistry and messenger RNA expression, and strongly suggest the existence of interactions between the basal ganglia direct and indirect pathways. (C) 2000 IBRO.

Percolation Effects on Adsorption-Desorption Hysteresis López, Raúl Horacio; Vidales, Ana Maria; Zgrablich, Giorgio In the present work we study how the adsorption−desorption hysteresis loop of a mesoporous-disordered medium represented by a three-dimensional dual site-bond model is affected by percolation for different kinds of site and bond distributions. The behavior of the threshold pressure for the evaporation process, as a function of the separation between the site and bond distributions and their dispersions, suggests a method to determine them from experimental adsorption−desorption hysteresis curves.

Biosurfactant-enhanced degradation of residual hydrocarbons from ship bilge wastes Olivera, Nelda Lila; Commendatore, Marta Graciela; Morán, A. C.; Esteves, Jose Luis The use of Bacillus subtilis O9 biosurfactant (surfactin) and of bioaugmentation to improve the treatment of residual hydrocarbons from ship bilge wastes was studied. A biodegradation experiment was conducted in aquaria placed outdoors under non-aseptic conditions. Three treatments were examined: culture medium plus bilge wastes, bioaugmentation with microorganisms from bilge wastes, and bioaugmentation plus biosurfactant. Samples were analyzed for viable counts, aliphatic and aromatic hydrocarbon concentrations, n-C17/pristane and n-C18/phytane ratios. While the addition of biosurfactant stimulated hydrocarbon degradation, bioaugmentation did not produce any remarkable effect. At day 10, the remaining percentages of aliphatic and aromatic hydrocarbons in aquaria, which received biosurfactant, were 6.8 and 7.2, respectively, while it took 20 days to reach comparable results with the other treatments. The biosurfactant did not affect the preferential biodegradation of n-C17/pristane and n-C18/phytane. This biosurfactant, which can be produced in a relatively simple and inexpensive process, is a promising alternative in the optimization of hydrocarbon waste treatment.

Surface Characterization of Li-Modified Platinum/Tin Catalysts for Isobutane Dehydrogenation Casella, Mónica Laura; Siri, Guillermo Jorge; Santori, Gerardo Fabian; Ferretti, Osmar Alberto; Ramırez Corredores, Maria Magdalena The superficial properties of different Pt/γ-Al2O3 catalysts, modified by the addition of tin and/or lithium, were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, BET, and 2-propanol transformation. The results obtained were correlated with the behavior of the catalysts in applied reactions such as the dehydrogenation of isobutane. To obtain very well defined bimetallic superficial phases, tin was introduced by means of surface organometallic chemistry on metals techniques and the nature of the bimetallic-active sites so obtained was compared with the ones prepared by conventional procedures. XPS measurements indicate that tin is present in both zeroth valent and oxidized states. The addition procedure of both tin and lithium has a marked influence on the characteristics of the surface of the catalysts. The order in which lithium is added generates solids having different properties in relation to texture, dispersion, and catalytic behavior, for both Pt and PtSn systems.