Novel Mechanism for Priming Aromatic Polyketide Synthases

AbstractIn this issue of Chemistry & Biology, a novel priming mechanism is proposed for aromatic polyketide biosynthesis, with an iterative type I polyketide synthase generating a starter unit primed for a type II polyketide synthase [6]. This novel priming system participates in hedamycin biosynthesis, a DNA alkylating agent

A quantum model of Schwarzschild black hole evaporation

We construct a one-loop effective metric describing the evaporation phase of a Schwarzschild black hole in a spherically symmetric null-dust model. This is achieved by quantising the Vaidya solution and by chosing a time dependent quantum state. This state describes a black hole which is initially in thermal equilibrium and then the equilibrium is switched off, so that the black hole starts to evaporate, shrinking to a zero radius in a finite proper time. The naked singularity appears, and the Hawking flux diverges at the end-point. However, a static metric can be imposed in the future of the end-point. Although this end-state metric cannot be determined within our construction, we show that it cannot be a flat metric

Hawking radiation by Kerr black holes and conformal symmetry

The exponential blueshift associated with the event horizon of a black hole makes conformal symmetry play a fundamental role in accounting for its thermal properties. Using a derivation based on two-point functions, we show that the spectrum of thermal radiation of scalar particles by Kerr (and Schwarzschild) black holes can be explicitly derived on the basis of a $2$-dimensional conformal symmetry arising in the wave equation near the horizon. This result reinforces the recently conjectured relation between Kerr geometry and a $2$-dimensional conformal field theory.Comment: Version published in Phys. Rev. Let

Inversion of the anomeric configuration of the transferred sugar during inactivation of the macrolide antibiotic oleandomycin catalyzed by a macrolide glycosyltransferase

AbstractMacrolides are a group of antibiotics structurally characterized by a macrocyclic lactone to which one or several deoxy-sugar moieties are attached. The sugar moieties are transferred to the different aglycones by glycosyltransferases (GTF). The OleI GTF of an oleandomycin producer, Streptomyces antibioticus, catalyzes the inactivation of this macrolide by glycosylation. The product of this reaction was isolated and its structure elucidated. The donor substrate of the reaction was UDP-α-D-glucose, but the reaction product showed a β-glycosidic linkage. The inversion of the anomeric configuration of the transferred sugar and other data about the kinetics of the reaction and primary structure analysis of several GTFs are compatible with a reaction mechanism involving a single nucleophilic substitution at the sugar anomeric carbon in the catalytic center of the enzyme

Empirical analysis of corporate credit lines

Since bank credit lines are a major source of corporate funding, we examine the determinants of credit line usage with a comprehensive database of Spanish corporate credit lines. A line’s default status is a key factor driving its usage, which increases as a firm’s financial condition worsens. Line usage decreases by roughly 10% for each year of its life. Lender characteristics, such as the number and length of a firm’s banking relationships, are found to affect a firm’s usage decisions, and credit line usage is found to be inversely related to macroeconomic condition

How does competition impact bank risk-taking?

A common assumption in the academic literature is that franchise value plays a key role in limiting bank risk-taking. As market power is the primary source of franchise value, reduced competition in banking markets has been seen as promoting banking stability. We test this hypothesis using data for the Spanish banking system. We find that standard measures of market concentration do not affect bank risk-taking. However, we find a negative relationship between market power measured using Lerner indexes based on bank-specific interest rates and bank risk. Our results support the franchise value paradig

Organocatalytic strategies for the development of the enantioselective inverse-electron-demand hetero-Diels-Alder reaction

Cycloaddition reactions, in particular Diels-Alder reactions, have attracted a lot of attention from organic chemists since they represent one of the most powerful methodologies for the construction of carbon-carbon bonds. In particular, inverse-electron-demand hetero-Diels-Alder reactions have been an important breakthrough for the synthesis of heterocyclic compounds. Among all their variants, the organocatalytic enantioselective version has been widely explored since the asymmetric construction of diversely functionalized scaffolds under reaction conditions encompassed within the green chemistry field is of great interest. In this review, a profound revision on the latest advances on the organocatalytic asymmetric inverse-electron demand hetero-Diels-Alder reaction is shownWe are grateful to the Spanish Government (CTQ2015-64561-R and RTI2018-095038-B-I00), “Comunidad de Madrid” and European Structural Funds (S2018/NMT-4367). J.A.F.-S. thanks the Spanish Government for a Ramón y Cajal contract. V.L.-M. thanks Universidad Autónoma de Madrid for a predoctoral fellowship (FPI-UAM

Design, manufacture and characterization of compact filter assemblies for radiofrequency applications

This paper presents the use of additive manufacturing in the design and fabrication of a non-planar fully 3Dprinted low-pass filter. The process implements stereolithographic 3D printing and copper electroplating to produce the necessary parts and their casing. The filter we produce acts as a demonstrator: we present the possibility of constructing building blocks and combining different elements into a full assembly for system integration. We introduce the "drop-and-screw" concept, which is implemented to mount the parts into a single connectorized assembly without the need for welding. The method we propose may be suitable for building other components by simply changing the building blocks. We pay special attention to the design of the constituent parts of the filter (a 3D conical inductor and a 3D capacitor), exploring new geometries to reduce the size of the final filter prototypes. The results demonstrate the potential of additive manufacturing in the construction of high-performance RF components and assemblies, and we present a modular prototype with a high degree of reconfigurability and multifunctionality

Catálogo nacional de los moluscos marinos de las aguas españolas

A checklist of marine Mollusca recorded in Spanish jurisdictional waters is presented, based on a thorough literature search and a limited input of recent field work. The list is detailed according to the five demarcations of the Marine Strategy Framework Directive (NOR, Spanish north coast; SUR, Spanish coast of the Gulf of Cádiz; ESAL, Strait of Gibraltar and Alboran Sea; LEBA, East coast of Spain and Balearic Islands; CAN, the Canary Islands). The list differentiates coastal species living from the supralittoral zone to the shelf break, deep-sea benthic or demersal species, and holoplanktonic species, and also distinguishes between non-indigenous species and species endemic to a particular demarcation. A total of 2466 marine Mollusca species have been reported from Spanish waters, of which 1126 are recorded only from waters surrounding the Iberian Peninsula, 498 are recorded from the Canaries only, and 842 are shared. That total number represents around 5.5% of the global marine molluscan richness. Shore and shelf species are the most numerous (1837), followed by deep-sea benthic species (490) and pelagic species (139), but the contribution of the deep-sea species is most noteworthy in NOR. All eight molluscan classes were represented, but solenogastres and scaphopods were notably more represented than usual in NOR. Species richness in SUR and ESAL was higher than would be expected from their areas, supporting the claim that Andalusian waters have an exceptionally diverse molluscan fauna. Thirteen species collected from INDEMARES cruises are here reported for the first time in Spanish waters. The species recorded in Spanish seas represent more than half of the 4340 species of Mollusca recorded within the scope of the European Register of Marine Species, making this the highest species count in European seas. The Canary Islands demarcation holds by far the largest number of endemic species (127), but special mention is needed regarding the ca. 20 species endemic to the Strait of Gibraltar, a highly anomalous chorotype in the marine realm. The number of non-indigenous species (38) is surprisingly low compared with that of species known in the Mediterranean Sea, amounting to hardly 1.5% of the total and supporting the view that a high number of native species tends to reduce invasion success. The list is seen as a much needed tool for the identification of priority areas for biodiversity conservation, but requires permanent attention and curating in order to remain up-to-date.Se presenta el catálogo actualizado de los moluscos marinos citados en las aguas jurisdiccionales españolas, basado en una exhaustiva revisión bibliográfica y en los hallazgos de campañas recientes. La lista se detalla para las cinco demarcaciones de la Directiva Marco sobre la Estrategia Marina (NOR: costas del norte de España; SUR: costas españolas del golfo de Cádiz, ESAL: estrecho de Gibraltar y mar de Alborán; LEBA: costas del este de España e islas Baleares; CAN: islas Canarias). En la lista se diferencia entre las especies costeras (las que viven desde la zona supralitoral hasta el borde de la plataforma continental), las especies bentónicas o demersales de aguas profundas y las especies holoplanctónicas, y también se indican las especies alóctonas y las que son endémicas para cada una de las demarcaciones. En total, se han citado 2.466 especies de moluscos marinos en aguas españolas, de las cuales 1.126 se conocen sólo en aguas peninsulares y baleares, 498 sólo en aguas canarias, mientras que 842 comparten ambas áreas. Ese número total representa alrededor del 5,5% de la riqueza específica global de moluscos marinos. Las especies costeras y de la plataforma continental son las más numerosas (1.837), seguidas de las especies de aguas profundas (490) y pelágicas (139), pero la contribución de las especies profundas es especialmente notable en NOR. Están representadas las ocho clases que comprende el filo Mollusca, con una destacable representación de los solenogastros y escafópodos en NOR. La riqueza de especies en SUR y ESAL es superior a la que cabría esperar de sus respectivas áreas, lo que apoya la afirmación de que las costas y aguas andaluzas albergan una malacofauna especialmente diversa. Trece especies recogidas en campañas del proyecto INDEMARES se citan aquí por primera vez en aguas españolas. Las especies registradas en los mares españoles suponen más de la mitad de las 4.340 especies de moluscos registradas en el ámbito geográfico del Registro Europeo de Especies Marinas, lo que supone el mayor número de especies de los países europeos. La demarcación de las islas Canarias es la que contiene con diferencia el mayor número de endemismos (127), pero merecen una mención especial las cerca de 20 especies endémicas del área del estrecho de Gibraltar, un corotipo muy anómalo en el medio marino. El número de especies alóctonas (38) es sorprendentemente bajo si lo comparamos con el número de especies que se consideran introducidas en el mar Mediterráneo, y representa apenas un 1,5 % del total, lo que apoya la idea de que un alto número de especies nativas tiende a reducir el éxito de las invasiones. La lista de especies que aquí se presenta constituye una herramienta muy necesaria para la identificación de áreas prioritarias de conservación de la biodiversidad, pero requiere una constante atención y actualización

Diffeomorphisms, Noether Charges and Canonical Formalism in 2D Dilaton Gravity

We carry out a parallel study of the covariant phase space and the conservation laws of local symmetries in two-dimensional dilaton gravity. Our analysis is based on the fact that the Lagrangian can be brought to a form that vanishes on-shell giving rise to a well-defined covariant potential for the symplectic current. We explicitly compute the symplectic structure and its potential and show that the requirement to be finite and independent of the Cauchy surface restricts the asymptotic symmetries.Comment: 14 pages, latex with psfig macro, one figur