N-Acetylglucosamine: Production and Applications

N-Acetylglucosamine (GlcNAc) is a monosaccharide that usually polymerizes linearly through (1,4)-β-linkages. GlcNAc is the monomeric unit of the polymer chitin, the second most abundant carbohydrate after cellulose. In addition to serving as a component of this homogeneous polysaccharide, GlcNAc is also a basic component of hyaluronic acid and keratin sulfate on the cell surface. In this review, we discuss the industrial production of GlcNAc, using chitin as a substrate, by chemical, enzymatic and biotransformation methods. Also, newly developed methods to obtain GlcNAc using glucose as a substrate in genetically modified microorganisms are introduced. Moreover, GlcNAc has generated interest not only as an underutilized resource but also as a new functional material with high potential in various fields. Here we also take a closer look at the current applications of GlcNAc, and several new and cutting edge approaches in this fascinating area are thoroughly discussed

The tertiary origin of the allosteric activation of E. coli glucosamine-6-phosphate deaminase studied by sol-gel nanoencapsulation of its T conformer.

The role of tertiary conformational changes associated to ligand binding was explored using the allosteric enzyme glucosamine-6-phosphate (GlcN6P) deaminase from Escherichia coli (EcGNPDA) as an experimental model. This is an enzyme of amino sugar catabolism that deaminates GlcN6P, giving fructose 6-phosphate and ammonia, and is allosterically activated by N-acetylglucosamine 6-phosphate (GlcNAc6P). We resorted to the nanoencapsulation of this enzyme in wet silica sol-gels for studying the role of intrasubunit local mobility in its allosteric activation under the suppression of quaternary transition. The gel-trapped enzyme lost its characteristic homotropic cooperativity while keeping its catalytic properties and the allosteric activation by GlcNAc6P. The nanoencapsulation keeps the enzyme in the T quaternary conformation, making possible the study of its allosteric activation under a condition that is not possible to attain in a soluble phase. The involved local transition was slowed down by nanoencapsulation, thus easing the fluorometric analysis of its relaxation kinetics, which revealed an induced-fit mechanism. The absence of cooperativity produced allosterically activated transitory states displaying velocity against substrate concentration curves with apparent negative cooperativity, due to the simultaneous presence of subunits with different substrate affinities. Reaction kinetics experiments performed at different tertiary conformational relaxation times also reveal the sequential nature of the allosteric activation. We assumed as a minimal model the existence of two tertiary states, t and r, of low and high affinity, respectively, for the substrate and the activator. By fitting the velocity-substrate curves as a linear combination of two hyperbolic functions with Kt and Kr as KM values, we obtained comparable values to those reported for the quaternary conformers in solution fitted to MWC model. These results are discussed in the background of the known crystallographic structures of T and R EcGNPDA conformers. These results are consistent with the postulates of the Tertiary Two-States (TTS) model

Variación estacional y nictímera en la distribución del zooplancton dominante en una laguna costera tropical

The dominant zooplankton of the La Mancha lagoon, Veracruz, Mexico, was analyzed with the objective of evaluating its seasonal and diel variability, as well as the influence of the main environmental variables on this variability. From May 2012 to April 2013, every month a 24-h cycle was completed, taking samples every 4 h, at the mouth of the lagoon. Simultaneously with zooplankton sampling, in situ environmental parameters such as temperature, dissolved oxygen, salinity, chlorophyll a and number of phytoplankton cells were recorded. We collected 54 taxa (mainly holoplankton) and 10 of them were considered dominant (total abundance > 0.5%). The zooplankton community was dominated mainly by two species of copepods (Acartia tonsa and Pseudodiaptomus pelagicus), as well as zoea larvae of brachyura (~85%). At seasonal level, the total abundance of zooplankton showed significant pulses throughout the year, one in February-March dominated by copepods and another in September-October, dominated by decapod larvae. On a diel scale, although total zooplankton abundance was significantly higher at night, only P. pelagicus, amphipods, megalopae, and other decapod larvae showed significant differences at this level. According to a Canonical Correspondence Analysis, the mouth stage (open/close), the number of cyanophytes and precipitation were the most important environmental factors in determining the abundance of the dominant zooplankton.El zooplancton dominante de la laguna La Mancha, Veracruz, México, fue analizado con el objetivo de evaluar su variabilidad estacional y nictímera, así como la influencia que sobre él ejercen las principales variables ambientales. De mayo 2012 a abril 2013, cada mes se realizó un ciclo de 24 h, tomando muestras cada 4 h, en la boca de la laguna. Simultáneamente a la toma de muestras de zooplancton, se registraron parámetros ambientales in situ como la temperatura, oxígeno disuelto, salinidad, clorofila a y número de células fitoplanctónicas. Se capturaron 54 taxa (principalmente del holoplancton) y 10 de ellos fueron considerados dominantes (abundancia total > 0,5%). La comunidad estuvo dominada por dos especies de copépodos (Acartia tonsa y Pseudodiaptomus pelagicus), así como por larvas zoea de braquiuros (~85%). La abundancia total del zooplancton mostró pulsos significativos a lo largo del año, uno en febreromarzo dominado por copépodos y otro en septiembre-octubre, dominado por larvas de decápodos. A pesar de que la abundancia total del zooplancton fue mayor en la noche, sólo P. pelagicus, anfípodos, megalopas y otras larvas de decápodo fueron significativos durante este período. De acuerdo con un Análisis de Correspondencia Canónica, el estado de la boca (abierta/cerrada), número de cianofitas y precipitación fueron los factores ambientales más importantes en la determinación de la abundancia del zooplancton dominant

Variación estacional y nictímera en la distribución del zooplancton dominante en una laguna costera tropical

Abstract: The dominant zooplankton of the La Mancha lagoon, Veracruz, Mexico, was analyzed with the objective of evaluating its seasonal and diel variability, as well as the influence of the main environmental variables on this variability. From May 2012 to April 2013, every month a 24-h cycle was completed, taking samples every 4 h, at the mouth of the lagoon. Simultaneously with zooplankton sampling, in situ environmental parameters such as temperature, dissolved oxygen, salinity, chlorophyll a and number of phytoplankton cells were recorded. We collected 54 taxa (mainly holoplankton) and 10 of them were considered dominant (total abundance > 0.5%). The zooplankton community was dominated mainly by two species of copepods (Acartia tonsa and Pseudodiaptomus pelagicus), as well as zoea larvae of brachyura (~85%). At seasonal level, the total abundance of zooplankton showed significant pulses throughout the year, one in February-March dominated by copepods and another in September-October, dominated by decapod larvae. On a diel scale, although total zooplankton abundance was significantly higher at night, only P. pelagicus, amphipods, megalopae, and other decapod larvae showed significant differences at this level. According to a Canonical Correspondence Analysis, the mouth stage (open/close), the number of cyanophytes and precipitation were the most important environmental factors in determining the abundance of the dominant zooplankton.Resumen: El zooplancton dominante de la laguna La Mancha, Veracruz, México, fue analizado con el objetivo de evaluar su variabilidad estacional y nictímera, así como la influencia que sobre él ejercen las principales variables ambientales. De mayo 2012 a abril 2013, cada mes se realizó un ciclo de 24 h, tomando muestras cada 4 h, en la boca de la laguna. Simultáneamente a la toma de muestras de zooplancton, se registraron parámetros ambientales in situ como la temperatura, oxígeno disuelto, salinidad, clorofila a y número de células fitoplanctónicas. Se capturaron 54 taxa (principalmente del holoplancton) y 10 de ellos fueron considerados dominantes (abundancia total > 0,5%). La comunidad estuvo dominada por dos especies de copépodos (Acartia tonsa y Pseudodiaptomus pelagicus), así como por larvas zoea de braquiuros (~85%). La abundancia total del zooplancton mostró pulsos significativos a lo largo del año, uno en febrero-marzo dominado por copépodos y otro en septiembre-octubre, dominado por larvas de decápodos. A pesar de que la abundancia total del zooplancton fue mayor en la noche, solo P. pelagicus, anfípodos, megalopas y otras larvas de decápodo fueron significativas durante este período. De acuerdo con un Análisis de Correspondencia Canónica, el estado de la boca (abierta/cerrada), número de cianofitas y precipitación fueron los factores ambientales más importantes en la determinación de la abundancia del zooplancton dominante

Reference values for the wild-type enzyme [20] and for the mutant F in solution.

a<p>Parameters obtained by fitting velocity against substrate concentration data to the MWC general equation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096536#pone.0096536-Henry1" target="_blank">[6]</a>.</p>b<p>Obtained by fitting velocity data to Hill equation.</p