Functional studies on oligotropha carboxidovorans molybdenum–copper CO dehydrogenase produced in escherichia coli

The Mo/Cu-dependent CO dehydrogenase (CODH) from Oligotropha carboxidovorans is an enzyme that is able to catalyze both the oxidation of CO to CO2 and the oxidation of H2 to protons and electrons. Despite the close to atomic resolution structure (1.1 Å), significant uncertainties have remained with regard to the reaction mechanism of substrate oxidation at the unique Mo/Cu center, as well as the nature of intermediates formed during the catalytic cycle. So far, the investigation of the role of amino acids at the active site was hampered by the lack of a suitable expression system that allowed for detailed site-directed mutagenesis studies at the active site. Here, we report on the establishment of a functional heterologous expression system of O. carboxidovorans CODH in Escherichia coli. We characterize the purified enzyme in detail by a combination of kinetic and spectroscopic studies and show that it was purified in a form with characteristics comparable to those of the native enzyme purified from O. carboxidovorans. With this expression system in hand, we were for the first time able to generate active-site variants of this enzyme. Our work presents the basis for more detailed studies of the reaction mechanism for CO and H2 oxidation of Mo/Cu-dependent CODHs in the future

Elusiveness of bishomoaromaticity in anionic systems: the bicyclo[3.2.1]octa-3,6-dien-2-yl anion

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How safe is vaginal birth after cesarean section for the mother and fetus?

Compared with planned repeat low-transverse cesarean section, vaginal birth after cesarean section (VBAC) is not associated with increased risk of maternal or neonatal mortality (strength of recommendation [SOR]: B). Morbidity is slightly increased, as evidenced by higher uterine rupture rates and some neonatal outcome measures (SOR: B)

Stabilization of the alleged bishomoromatic bicyclo[3.2.1]octa-2,6-dienyl anion by counterion interactions and by hyperconjugation

Hyperconjugation and inductive effects, rather than homoaromaticity, are responsible for the stabilization of the title anion in the gas phase; interaction of the double bond with the Li+ gegenion in the endo geometry contributes additionally in solution

Strategic Long-Term Financial Risks: Single Risk Factors

The question of the measurement of strategic long-term financial risks is of considerable importance. Existing modelling instruments allow for a good measurement of market risks of trading books over relatively small time intervals. However, these approaches may have severe deficiencies if they are routinely applied to longer time periods. In this paper we give an overview on methodologies that can be used to model the evolution of risk factors over a one-year horizon. Different models are tested on financial time series data by performing backtesting on their expected shortfall prediction

Räumliche und zeitliche Visualisierung als Smart-City-Planungswerkzeug

Die steigende Bevölkerung und der starke Zuzug in die urbanen Ballungsräume ist eine große Herausforderung für die Akteure der Planungswelt. Um ressourcenschonende Planungen voranzutreiben, ist eine innere Entwicklung der urbanen Systeme zielführend. Dabei ist neben der Aufspürung und Nutzung von Flächenreserven, die Nutzung und der Ausbau bestehender Versorgungsinfrastruktursysteme eine Möglichkeit für nachhaltige Entwicklungen. Dies stellt eine komplexe Planungsaufgabe für Planer und Entscheidungsträger dar, die das Zusammenwirken von Planungsakteuren unterschiedlichster Domänen erfordert. Innerhalb des interdisziplinären Forschungsprojektes URBEM (Urbanes Energie- und Mobilitätssystem) wurde ein visuelles Planungs- und Entscheidungsunterstützungswerkzeug, die URBEMVisualisierung, entwickelt. Diese webbasierte Umgebung bietet eine Arbeits- und Kommunikationsplattform für Domänenexperten und Stakeholder zur Unterstützung komplexer Planungsprozesse. Die URBEMVisualisierung erlaubt domänenspezifische Simulationsergebnisse räumlich zu verorten, visuelle Übersichten zu generieren und ein urbanes Gesamtsystem mit Hilfe der räumlichen Überlagerung von Informationen unterschiedlichster Versorgungsträgerstrukturen im Bereich Energie und Mobilität zu untersuchen. Dies bietet den Planern eine Grundlage um Probleme im Raum und in der Zeit fest zu machen und gezielte Maßnahmen zur Entwicklung smarter Lebensräume aufzuzeigen. Die Möglichkeiten der URBEM Visualisierung werden im folgenden Beitrag anhand von Modellergebnissen aus der Domäne Mobilität illustriert

Reconstitution of Molybdoenzymes with Bis-Molybdopterin Guanine Dinucleotide Cofactors

International audienceMolybdoenzymes are ubiquitous, and play important roles in all kingdoms of life. The enzymes' cofactors comprise the metal molybdenum, a special organic ligand system called molybdopterin (MPT), additional small ligands like water, hydroxide, oxo-, sulfido-or selenido-functions and, in some enzymes, a coordination to the peptide chain of the protein via an amino acid ligand (e.g. serine, aspartate, cysteine or selenosysteine). The so-called molybdenum cofactor (Moco) is deeply buried in the protein at the end of a narrow funnel giving access only to the substrate. In 1974 an assay was developed by Nason and coworkers using the pleotrophic Neurospora crassa mutant nit-1 for the reconstitution of molybdoenzyme activities from crude extracts. These studies lead to the understanding that Moco is the common element in all molybdoenzymes from different organisms. The assay has been further developed since using specific molybdenum enzymes as source of Moco for the reconstitution of diverse purified apo-molybdoenzymes. Alternatively, the molybdenum cofactor can be synthesized in vitro from stable intermediates and can be inserted into apo-molybdoenzymes by the aid of specific Moco-binding chaperones. A general working protocol is described here for the insertion of the bis-molybdopterin guanine dunucleotide cofactor (bis-MGD) into its target molybdoenzyme using the example of Escherichia coli TMAO reductase.

Precise Experimental Investigation of Eigenmodes in a Planar Ion Crystal

The accurate characterization of eigenmodes and eigenfrequencies of two-dimensional ion crystals provides the foundation for the use of such structures for quantum simulation purposes. We present a combined experimental and theoretical study of two-dimensional ion crystals. We demonstrate that standard pseudopotential theory accurately predicts the positions of the ions and the location of structural transitions between different crystal configurations. However, pseudopotential theory is insufficient to determine eigenfrequencies of the two-dimensional ion crystals accurately but shows significant deviations from the experimental data obtained from resolved sideband spectroscopy. Agreement at the level of 2.5 x 10^(-3) is found with the full time-dependent Coulomb theory using the Floquet-Lyapunov approach and the effect is understood from the dynamics of two-dimensional ion crystals in the Paul trap. The results represent initial steps towards an exploitation of these structures for quantum simulation schemes.Comment: 5 pages, 4 figures, supplemental material (mathematica and matlab files) available upon reques