Unusual long-term stability of enzymatic bioelectrocatalysis in organic solvents

Organic solvent tolerant enzymes are of tremendous importance for the pharmaceutical industry in search of high added-value chemicals. However, enzymes exhibit usually weak long-term activity and stability in various media. Here, we report a general strategy allowing stabilizing and keeping enzymes active in mixed-solvent systems upon immobilization on an electrode surface. It consists in the combination of an engineered solventtolerant enzyme, combined with fine-tuned osmium-based redox polymers where the concentration of osmium complex has been specifically tuned to minimize its deswelling, associated with the use of porous gold electrodes. This approach is validated with bilirubin oxidase as a model system. This copper enzyme is able to oxidize a wide range of substrates, combined with the reduction of O-2 to water. While all other enzymatic systems irreversibly lose their activity and stability in the presence of 7.5 M methanol or below, this optimized enzymatic system stays functional in 12.5 M methanol with no loss in current density. It exhibits a half-life of more than 8 days, which is unprecedented in the literature. We show that this electrode can also operate in DMSO, dioxane, acetonitrile and acetone, thus opening up a very wide variety of applications in the field of bioelectrocatalysis and bioelectrosynthesis

Redox-Polymer-Wired [NiFeSe] Hydrogenase Variants with Enhanced O2 Stability for Triple-Protected High-Current-Density H2-Oxidation Bioanodes

Variants of the highly active [NiFeSe] hydrogenase from D. vulgaris Hildenborough that exhibit enhanced O2 tolerance were used as H2-oxidation catalysts in H2/O2 biofuel cells. Two [NiFeSe] variants were electrically wired by means of low-potential viologen-modified redox polymers and evaluated with respect to H2-oxidation and stability against O2 in the immobilized state. The two variants showed maximum current densities of (450±84) μA cm−2 for G491A and (476±172) μA cm−2 for variant G941S on glassy carbon electrodes and a higher O2 tolerance than the wild type. In addition, the polymer protected the enzyme from O2 damage and high-potential inactivation, establishing a triple protection for the bioanode. The use of gas-diffusion bioanodes provided current densities for H2-oxidation of up to 6.3 mA cm−2. Combination of the gas-diffusion bioanode with a bilirubin oxidase-based gas-diffusion O2-reducing biocathode in a membrane-free biofuel cell under anode-limiting conditions showed unprecedented benchmark power densities of 4.4 mW cm−2 at 0.7 V and an open-circuit voltage of 1.14 V even at moderate catalyst loadings, outperforming the previously reported system obtained with the [NiFeSe] wild type and the [NiFe] hydrogenase from D. vulgaris Miyazaki F.inpres

Uphill production of dihydrogen by enzymatic oxidation of glucose without an external energy source

Chemical systems do not allow the coupling of energy from several simple reactions to drive a subsequent reaction, which takes place in the same medium and leads to a product with a higher energy than the one released during the first reaction. Gibbs energy considerations thus are not favorable to drive e.g., water splitting by the direct oxidation of glucose as a model reaction. Here, we show that it is nevertheless possible to carry out such an energetically uphill reaction, if the electrons released in the oxidation reaction are temporarily stored in an electromagnetic system, which is then used to raise the electrons’ potential energy so that they can power the electrolysis of water in a second step. We thereby demonstrate the general concept that lower energy delivering chemical reactions can be used to enable the formation of higher energy consuming reaction products in a closed system

The endogenous retrovirus ENS-1 provides active binding sites for transcription factors in embryonic stem cells that specify extra embryonic tissue

<p>Abstract</p> <p>Background</p> <p>Long terminal repeats (LTR) from endogenous retroviruses (ERV) are source of binding sites for transcription factors which affect the host regulatory networks in different cell types, including pluripotent cells. The embryonic epiblast is made of pluripotent cells that are subjected to opposite transcriptional regulatory networks to give rise to distinct embryonic and extraembryonic lineages. To assess the transcriptional contribution of ERV to early developmental processes, we have characterized <it>in vitro </it>and <it>in vivo </it>the regulation of ENS-1, a host adopted and developmentally regulated ERV that is expressed in chick embryonic stem cells.</p> <p>Results</p> <p>We show that <it>Ens-1 </it>LTR activity is controlled by two transcriptional pathways that drive pluripotent cells to alternative developmental fates. Indeed, both Nanog that maintains pluripotency and Gata4 that induces differentiation toward extraembryonic endoderm independently activate the LTR. Ets coactivators are required to support Gata factors' activity thus preventing inappropriate activation before epigenetic silencing occurs during differentiation. Consistent with their expression patterns during chick embryonic development, Gata4, Nanog and Ets1 are recruited on the LTR in embryonic stem cells; in the epiblast the complementary expression of Nanog and Gata/Ets correlates with the <it>Ens-1 </it>gene expression pattern; and Ens-1 transcripts are also detected in the hypoblast, an extraembryonic tissue expressing Gata4 and Ets2, but not Nanog. Accordingly, over expression of Gata4 in embryos induces an ectopic expression of <it>Ens-1</it>.</p> <p>Conclusion</p> <p>Our results show that <it>Ens-1 </it>LTR have co-opted conditions required for the emergence of extraembryonic tissues from pluripotent epiblasts cells. By providing pluripotent cells with intact binding sites for Gata, Nanog, or both, <it>Ens-1 </it>LTR may promote distinct transcriptional networks in embryonic stem cells subpopulations and prime the separation between embryonic and extraembryonic fates.</p

Mise en place de l'observatoire du développement composante 1. Constitution d'un système d'information sur le secteur agricole de la zone PRASAC : rapport de mission au Tchad, Cameroun du 07 au 23 novembre 1999

Cette mission s'inscrit dans le cadre de la composante 1 du PRASAC: «Mise en place d'un Observatoire du Développement» dont l'objectif prioritaire est de mettre à disposition des partenaires du développement, un outil informatique permettant d'étudier et d'analyser les grandes dynamiques régionales pour mieux comprendre le fonctionnement de cet espace. Suite aux orientations prises lors des différents ateliers de programmation du PRASAC, l'Observatoire du Développement a été conçu comme un centre intégrateur, un centre d'analyse et un centre d'information à destination des chercheurs et des opérateurs du développement. Il s'appuie sur le laboratoire régional de géomatique de Bangui placé sous la tutelle de l'Institut Centrafricain de la Recherche Agronomique (ICRA) lequel a constitué une banque de données intégrée dans un Système d'Information Géographique (SIG) appelée SISAC (Système d'Information sur le Secteur Agricole de la zone des Savanes d'Afrique Centrale). La diffusion des produits, essentiellement cartographiques, issus des analyses spatiales effectuées à l'aide du SIG doit concourir à générer des contributions et commentaires techniques de la part des Ministères / agences techniques partenaires. De plus, ces produits doivent servir de matière première à l'identification de projets de recherche. (Résumé d'auteur