Thermodynamic performance of coupled enzymatic reactions: A chemical kinetics model for analyzing cotransporters, ion pumps, and ATP synthases

[EN]Previous research has suggested that molecular energy converters such as ATP synthases, ion pumps, and cotransporters operate via spatially separate pathways for free energy donor and acceptor reactions linked by a protein molecule. We present a chemical kinetics model based on these works, with the basic assumption that all molecular energy converters can be thought of as linked enzymatic reactions, one running downhill the chemical potential gradient and driving the other uphill. To develop the model we first look at how an enzyme process can be forced to go backwards using a basic kinetic model. We then use these findings to suggest a thermodynamically consistent method of linking two enzymatic reactions. Finally, in the context of the aforementioned energy converters, the thermodynamic performance of the resulting model is thoroughly investigated and the obtained results are contrasted with experimental data.Conacyt-M´exico, Grant No. CDF19-568462; University of Salamanca, Contract No. 0218 463AB0

Construcción de relaciones gráficas intuitivas en el estudio de la variación y la acumulación apoyadas con tecnología digital

Esta investigación se desarrolla a través de un estudio cualitativo, en proceso, que aborda la enseñanza del Cálculo, al cual entendemos de acuerdo al currículo de bachillerato, como el estudio de la variación y la acumulación. En el diseño experimental recolectamos datos aplicando cuestionarios y analizando videos de las actividades aplicadas. Se trabaja con alumnos de bachillerato de 15 y 16 años utilizando tecnología digital: un sensor de movimiento y applets de gráficas ligadas dinámicas. Nuestros propósitos son: estudiar que conexiones son esenciales en el estudio de la variación y la acumulación; explorar su viabilidad para la enseñanza en bachillerato. Nuestros principales resultados indican que se puede favorecer la construcción de relaciones entre pares: acumulación o área bajo una curva y distancia recorrida; pendiente y velocidad; continuidad y tiempo; gráfica de distancia tiempo con picos y su imposibilidad de reproducir los picos caminando frente al sensor, dando de éste último par evidencia experimental; pares entre elementos geométricos y físicos, con los cuales nos valemos de un elemento del par para hacer sentido del otro

Link between optimization and local stability of a low-dissipation heat engine: Dynamic and energetic behaviors

[EN]In the present paper we study the connection between local stability and energetic properties in low-dissipation heat engines operating in the maximum-power and maximum-compromise ( ) regimes. We consider two different feedback regulatory pathways: (1) one in which restitutive forces linearly depend on the deviations from the stationary values of the heat exchanges with the hot and cold reservoirs and (2) another where restitutive forces depend on the deviations from the stationary values of the power output and the heat outflux into the cold reservoir. The first dynamics leads to an isolated stable point while in the second one the system is metastable. Further analysis of random perturbations from the steady state gives valuable information about the dynamic behavior of thermodynamic properties like entropy, power, and efficiency in both operation regimes

Local-stability analysis of a low-dissipation heat engine working at maximum power output

[EN]In this paper we address the stability of a low-dissipation (LD) heat engine (HE) under maximum power conditions. The LD system dynamics are analyzed in terms of the contact times between the engine and the external heat reservoirs, which determine the amount of heat exchanged by the system. We study two different scenarios that secure the existence of a single stable steady state. In these scenarios, contact times dynamics are governed by restitutive forces that are linear functions of either the heat amounts exchanged per cycle, or the corresponding heat fluxes. In the first case, according to our results, preferably locating the system irreversibility sources at the hot-reservoir coupling improves the system stability and increases its efficiency. On the other hand, reducing the thermal gradient increases the system efficiency but deteriorates its stability properties, because the restitutive forces are smaller. Additionally, it is possible to compare the relaxation times with the total cycle time and obtain some constraints upon the system dynamics. In the second case, where the restitutive forces are assumed to be linear functions of the heat fluxes, we find that although the partial contact time presents a locally stable stationary value, the total cycle time does not; instead, there exists an infinite collection of steady values located in the neighborhood of the fixed point, along a one-dimensional manifold. Finally, the role of dissipation asymmetries on the efficiency, the stability, and the ratio of the total cycle time to the relaxation time is emphasized. © 2017 American Physical Society.Consejo Nacional de Ciencia y Tecnología Instituto Politécnico Nacional Ministry of Economy, Industry and Competitivenes

Evaluation of the anti-inflammatory capacity of beta-sitosterol in rodent assays

Background: Beta-sitosterol (BS) is a compound discovered to be present in numerous plants. A number of interesting biomedical properties have been attributed to BS, including immuno-modulating and anti-inflammatory activities. Therefore, the aim of this report was to evaluate its anti-inflammatory capacity by applying various rodent experimental tests.Methods. To carry out the objective of the study we applied the methods indicated here. Two of the adopted methods were based on the passive reverse Arthus reaction: the rat paw edema test and the rat pleurisy assay. We also applied two methods related with the non-specific acute inflammation: the mouse ear edema test, and the mouse mieloperoxidase activity assay.Results. The results obtained in all tests established a significant anti-inflammatory potential of BS. In the rat paw edema test we found an inhibitory effect which goes from 50-70%; in the rat pleurisy assay our findings with respect to the volume of pleural exuded showed a reduction of 46%, as well as a 20% low amount of neutrophils in comparison with the level of the control group. In the mouse ear edema test we found a mean inflammatory inhibition of 75%, and with respect to mieloproxidase activity the results showed a significant inhibition induced by the three doses of BS.Conclusions. In the present study we determined a potent anti-inflammatory capacity of BS in specific and nonspecific types of acute inflammation in rodents.Keywords: Beta-sitosterol, anti-inflammatory assays, mouse, ra

Paratuberculosis ovina: factores de riesgo asociados al manejo del pie de cría y de las heces en unidades de producción pecuárias: Ovine paratuberculosis: prevalence and risks associated with animal breeding stock and management of feces in livestock production units

El objetivo del estudio fue determinar la prevalencia y los factores de riesgo asociados a paratuberculosis con relación al pie de cría y manejo de las heces en los corrales. Se llevó a cabo un estudio epidemiológico de tipo transversal. Se trabajo en  66 Unidades de Producción Pecuaria (UPP) de ovinos en el estado de Guanajuato, México. Se tomó una muestra de sangre por animal (n=1387) para llevar a cabo el diagnóstico serológico de Map con la prueba de Inmuno difusión en agar gel, y se aplicó un cuestionario por UPP. Todos los resultados fueron integrados en una base de datos para su análisis epidemiológico con el  programa estadístico STATA® 7. Las UPP que compran sementales  tienen una prevalencia de 42.4% y de hembras del 40% con una OR de 4 y 3. Las UPP que prestan a los sementales tienen una prevalencia del 42.3% y OR de 3. Las UPP que limpian los corrales en un periodo de tiempo que va de los dos meses al año, presentaron un 45% y OR 4.3. En las UPP donde las heces permanecen acumuladas, presentaron una prevalencia del 66.6% y una OR de 30. El manejo sanitario debe estar enfocado en tratar de disminuir la presencia de enfermedades crónico infecciosas como lo es la paratuberculosis, ya que su propagación lenta y su curso crónico en los rebaños, ponen en riesgo al pie de cría y su capacidad productiva y reproductiva

Fermentation kinetics and in vitro degradation of three native creeping legumes of the municipality of Cuajinicuilapa, Guerrero

El objetivo del estudio fue evaluar la cinética de fermentación y la degradación in vitro de tres leguminosas nativas del municipio de Cuajinicuilapa, Guerrero. Los sustratos fueron vainas, hojas y planta completa de centrosema (Centrosema plumiere), frijolillo (Phaseolus lunatus var. silvester) y frijolillo-tamarindo (Phaseolus lunatus). Los biodigestores contenían 0.5 g de un sustrato y 50 ml de medio de cultivo. Los biodigestores se incubaron en baño maría a 39 °C por 72 h. La producción de gas se midió a las 0, 2, 4, 6, 9, 12, 24, 36, 48 y 72 h. La producción de gas se usó para obtener los parámetros volumen máximo (Vm), tasa de producción de gas (S) y tiempo lag (λ). La degradación de la materia seca (DEGMS) y degradación de la fibra detergente neutra (DEGFDN) se determinaron por diferencia de peso. El análisis estadístico fue un diseño completamente al azar con arreglo factorial 3x3. La vaina de centrosema produjo el mayor Vm, la hoja de centrosema y vaina de frijolillo-tamarindo la mayor S, la hoja, planta y vaina de centrosema el menor λ, la vaina de centrosema la mayor DEGMS y DEGFDN. La hoja de centrosema presentó mayor Vm y S, así como menor λ que las hojas de frijolillo y frijolillo-tamarindo. La vaina de centrosema mostró mayor Vm, DEGMS y DEGFDN; además, menor λ que las vainas de frijolillo y frijolillo-tamarindo (pThe objective was to evaluate the fermentation kinetics and the in vitro degradation of the physiological parts of three native legumes of the municipality of Cuajinicuilapa, Guerrero. The substrates were pods, leaves and complete plant of centrosema (Centrosema plumiere), bean (Phaseolus lunatus var. silvester) and bean-tamarind (Phaseolus lunatus). The biodigestor contained 0.5 g of a substrate and 50 ml of culture medium. The biodigestor were incubated in a water bath at 39 °C for 72 h. Gas production was measured at 0, 2, 4, 6, 9, 12, 24, 36, 48 and 72 h. The gas production was used to obtain the parameters maximum volume (mV), rate of gas production (S) and time lag (λ). Dry matter degradation (DEGDM) and degradation of the neutral detergent fibre (DEGNDF) were determined by weight difference. The statistical analysis was a completely randomized design within a 3x3 factorial arrangement. The centrosema pod produced the higher mV, the centroid leaf and bean-tamarind pod the higher S, the leaf, plant and pod of centrosema the less λ, the pod of centrosema the higher DEGDM and DEGNDF. The centrosema leaf presented higher mV and S and less λ than the leaves of bean and bean-tamarind. The centroid sheath showed higher mV, DEGDM and DEGNDF and less λ than the bean and bean-tamarind pods (p<0.05). It is concluded that the evaluated components of the native creeping legume Centrosema plumiere presented better nutritional response in the in vitro evaluation than the other legumes

Antigenotoxic Effect of Chamomilla recutita (L.) Rauschert Essential Oil in Mouse Spermatogonial Cells, and Determination of Its Antioxidant Capacity in Vitro

Chamomilla recutita (L.) Rauschert (Asteraceae), popularly known as chamomile, is a plant used in traditional medicine for various therapeutic purposes. Chamomile essential oil (CEO) is particularly known to inhibit the genotoxic damage produced by mutagens in mice somatic cells. The aim of this research was to determine the inhibitory potential of CEO on the genotoxic damage produced by daunorubicin (DAU) in mice germ cells. We evaluated the effect of 5, 50, and 500 mg/kg of essential oil on the rate of sister chromatid exchange (SCE) induced in spermatogonia by 10 mg/kg of the mutagen. We found no genotoxicity of CEO, but detected an inhibition of SCE after the damage induced by DAU; from the lowest to the highest dose of CEO we found an inhibition of 47.5%, 61.9%, and 93.5%, respectively. As a possible mechanism of action, the antioxidant capacity of CEO was determined using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method and ferric thiocyanate assays. In the first test we observed a moderate scavenging potential of the oil; nevertheless, the second assay showed an antioxidant capacity similar to that observed with vitamin E. In conclusion, we found that CEO is an efficient chemoprotective agent against the damage induced by DAU in the precursor cells of the germinal line of mice, and that its antioxidant capacity may induce this effect

Caracterización química de aguas subterráneas en pozos y un distribuidor de agua de Zimapán, Estado de Hidalgo, México

The characterization of the ground waters that supply the general distributor of water of Zimapán city, State of Hidalgo, Mexico and the distributor itself, is carried out in this work. Eleven sampling points have been selected in which 28 physical-chemical parameters of the collected water have been determined during 10 samplings distributed along one year (March of 1999-March of 2000). In general these waters present normal physicalchemical properties and are classified as bicarbonated-calcic and bicarbonated-mixed waters, with low levels  of sulfates, chlorides, sodium and potassium; with very high concentrations of As up to 550 ? g· l-1, exceeding in more than 10 times the norm NOM-127-SSA1-1994 for drinking water (Secretaria de Salud, 1996). The study of temporal variation showed significant seasonal variations with an increase in the concentrations of the total elements during the months of February and March (season of scarce rains) and a decrease in the months of April to July (season of rains), this is probably due to dilution effects caused by pluvial precipitation, which is infiltrated to the phreatic mantle. In addition, the supply wells and the points of sampling of the general distributor were correlated by means of a multi-varied analysis of physical-chemical properties.En este trabajo se llevó a cabo la caracterización de las aguas subterráneas que abastecen al distribuidor general de agua de la ciudad de Zimapán Hidalgo, México y del propio distribuidor. Para ello se seleccionaron 11 puntos de muestreo en los que se determinaron 28 parámetros fisico-químicos de las aguas colectadas durante 10 muestreos distribuidos a lo largo de un año (marzo de 1999-marzo de 2000). De forma general, estas aguas presentaron propiedades fisicoquímicas normales clasificadas como aguas bicarbonatadas-cálcicas y bicarbonatadas-mixtas con bajos niveles de sulfatos, cloruros, sodio y potasio; pero presentaron concentraciones de As muy elevadas de hasta 550 ? g· l-1, superando en más de 10 veces la norma NOM-127-SSA1-1994 para aguas potables (Secretaria de Salud, 1996). En el estudio de variación temporal se observaron cambios significativos de carácter estacional con incremento en las concentraciones de los elementos totales durante los meses de febrero y marzo (temporada de escasas lluvias) y una disminución de los mismos durante el período abril a julio (temporadas de lluvias), ésto último probablemente debido a efectos de la dilución causada por la precipitación pluvial que se infiltra al manto freático, además, se han correlacionado los pozos de suministro y los puntos de muestreo del distribuidor general mediante un análisis multivariado de las propiedades fisicoquímicas

Chiapas : entre el autoritarismo y la transición democrática, desde Acteal hasta el diálogo EZLN y sociedad civil

Obra cuya intención es dar cuenta de los diversos actores sociales involucrados en el conflicto de Chiapas, a nivel político, económico y sociocultural. El texto recupera un taller de análisis de coyuntura sobre el tema, realizado en agosto de 1998.ITESO, A.C