An allylic ketyl radical intermediate in clostridial amino-acid fermentation

The human pathogenic bacterium Clostridium difficile thrives by the fermentation of l-leucine to ammonia, CO(2), 3-methylbutanoate and 4-methylpentanoate under anaerobic conditions. The reductive branch to 4-methylpentanoate proceeds by means of the dehydration of (R)-2-hydroxy-4-methylpentanoyl-CoA to 4-methylpent-2-enoyl-CoA, which is chemically the most demanding step. Ketyl radicals have been proposed to mediate this reaction catalysed by an iron-sulphur-cluster-containing dehydratase, which requires activation by ATP-dependent electron transfer from a second iron-sulphur protein functionally similar to the iron protein of nitrogenase. Here we identify a kinetically competent product-related allylic ketyl radical bound to the enzyme by electron paramagnetic resonance spectroscopy employing isotope-labelled (R)-2-hydroxy-4-methylpentanoyl-CoA species. We also found that the enzyme generated the stabilized pentadienoyl ketyl radical from the substrate analogue 2-hydroxypent-4-enoyl-CoA, supporting the proposed mechanism. Our results imply that also other 2-hydroxyacyl-CoA dehydratases and the related benzoyl-CoA reductases-present in anaerobically living bacteria-employ ketyl radical intermediates. The absence of radical generators such as coenzyme B12, S-adenosylmethionine or oxygen makes these enzymes unprecedented in biochemistry.     

The first hominin of Europe

The earliest hominin occupation of Europe is one of the most debated topics in palaeoanthropology. However, the purportedly oldest of the Early Pleistocene sites in Eurasia lack precise age control and contain stone tools rather than human fossil remains. Here we report the discovery of a human mandible associated with an assemblage of Mode 1 lithic tools and faunal remains bearing traces of hominin processing, in stratigraphic level TE9 at the site of the Sima del Elefante, Atapuerca, Spain. Level TE9 has been dated to the Early Pleistocene (approximately 1.2-1.1 Myr), based on a combination of palaeomagnetism, cosmogenic nuclides and biostratigraphy. The Sima del Elefante site thus emerges as the oldest, most accurately dated record of human occupation in Europe, to our knowledge. The study of the human mandible suggests that the first settlement of Western Europe could be related to an early demographic expansion out of Africa. The new evidence, with previous findings in other Atapuerca sites (level TD6 from Gran Dolina), also suggests that a speciation event occurred in this extreme area of the Eurasian continent during the Early Pleistocene, initiating the hominin lineage represented by the TE9 and TD6 hominins.     

Semiotic Vision of Ideologies

A semiotic theory of systems derived from language would have the purpose of classifying all the systems of linguistic expression: philosophy, ideology, myth, poetry, art, as much as the dream, lapsus, and free association in a pluridimensional matrix that will interact with many diversified fields. In each one of these discourses it is necessary to consider a plurality of questions, the essence of which will only be comprehensible by the totality; it will be necessary to ask, in the first place, what will be the purpose of this language, what function does it fulfill and for which reason has it been constructed. The concept of World vision (WV) is introduced and its relation with Generalized Collective Conscience (GCC) and Particularized Collective Conscience. Culture implies a particular WV. Culture creates GCC. The semantic field is a structure that formalizes the units of a certain culture constituting a portion of the vision of the Reality that owns this culture. An ecological case is explained.     

Experience in combining subjective and quantitative forecasts of open market rates

This paper presents a method of combining subjective information from open-market operators with results from a time-series forecasting model. Empirical results of forecasts for interest rates of bank reserves are presented.     

Histamine release and mast cell degranulation induced by 2-4 dinitrophenol in rat tissues

Resumen El 2–4-dinitrofenol es capaz de producir degranulación rápida aunque parcial de mastocitos y liberación de histamina de los tejidos de la rata in vitro. Estos efectos solamente pueden ser demostrados en tejidos mantenidos a baja temperatura antes del tratamiento; son inhibidos por glucosa. La estimulación del consumo de oxígeno no parece ser la causa de los efectos del dinitrofenol.     

Forecasting the conditional covariance matrix of a portfolio under long‐run temporal dependence

Long‐range persistence in volatility is widely modelled and forecast in terms of the so‐called fractional integrated models. These models are mostly applied in the univariate framework, since the extension to the multivariate context of assets portfolios, while relevant, is not straightforward. We discuss and apply a procedure which is able to forecast the multivariate volatility of a portfolio including assets with long memory. The main advantage of this model is that it is feasible enough to be applied on large‐scale portfolios, solving the problem of dealing with extremely complex likelihood functions which typically arises in this context. An application of this procedure to a portfolio of five daily exchange rate series shows that the out‐of‐sample forecasts for the multivariate volatility are improved under several loss functions when the long‐range dependence property of the portfolio assets is explicitly accounted for. Copyright © 2006 John Wiley & Sons, Ltd.