Large gallanes and the PSEPT theory: a theoretical study of Ga n H n+2 clusters (n?=?7–9)

Do alanes Al(n)H(n+2) and gallanes Ga(n)H(n+2) satisfy the polyhedral skeletal electron pair theory (PSEPT)? Taking into account previous work on this question, this paper provides a convincing answer and proposes the reformulation of the (n + 1) electron pairs rule of Wade and Mingos (W-M) for such systems. Following recent studies of tetra-, penta-, hexa-, hepta-, octa-, and nonaalanes as well as valence-isoelectronic/related gallanes, in this paper we present an analysis of the hydrides of aluminum and gallium A(n)H(n+2) (A = Al, Ga and n = 7-9). The aim is still to examine the applicability of PSEPT, especially the W-M rule, to these clusters. Exploration of the total potential energy surfaces (PESs) of hepta-, octa-, and nonagallanes shows that the absolute minima have a nido-like polyhedron arrangement. Unlike the smaller Ga(n)H(n+2) (n = 4, 5, 6), it seems that the size of the cluster largely dictates its preferred geometry. Although none of them have closed (totally triangular) cages, these clusters exhibit significant compactness, comparable to borane double anions, B(n)H(n) (2-), which are the archetypes for the PSEPT theory.     

Core-shell structured PEO-chitosan nanofibers by coaxial electrospinning

Core-shell structured PEO-chitosan nanofibers have been produced using a coaxial electrospinning setup. PEO and chitosan solutions, both in an aqueous acetic acid solvent, were used as the inner (core) and outer (shell) layer, respectively. Uniform-sized defect-free nanofibers of 150-190 nm diameter were produced. In addition, hollow nanofibers could be obtained subsequent to PEO washing of the membranes. The core-shell nanostructure and existence of chitosan on the shell layer were confirmed by TEM images obtained before and after washing the PEO content with water. The presence of chitosan on the surface of the composite nanofibers was further supported by XPS studies. The chitosan and PEO compositions in the nanofibrous mats were determined by TGA analysis, which were similar to their ratio in the feed solutions. The local compositional homogeneity of the membranes and the efficiency of the washing step to remove PEO were also verified by FTIR. In addition, DSC and XRD were used to characterize the crystalline structure and morphology of the co-electrospun nonwoven mats. The prepared coaxial nanofibers (hollow and solid) have several potential applications due to the presence of chitosan on their outer surfaces.     

Pravastatin: A tool for investigating the availability of mevalonate metabolites for primary and secondary metabolism in Catharanthus roseus cell suspensions

In the C20 strain of Catharanthus roseus , 2,4-dichlorophenoxyacetic acid (2,4-D) reduces alkaloid accumulation by inhibiting the synthesis of precursors of alkaloid terpenoids. However, the presence of this growth regulator is necessary to promote growth, as measured in terms of dry weight and sterol content. The terpenoid metabolism implicated in the accumulation of alkaloids would therefore be the target of 2,4-D inhibition and not the metabolism leading to sterol biosynthesis. The specific inhibition by pravastatin of 3-hydroxy-3-methylglutaryl CoA reductase (EC 1.1.1.34), the enzyme that catalyses mevalonate synthesis, enables the limitation of mevalonate on sterol content and on alkaloid accumulation to be studied. In presence of pravastatin cells are supplied with labelled mevalonate. Under these conditions the mevalonate is incorporated into sterols but not into alkaloids accumulated in the absence of 2,4-D. The inhibition of sterol biosynthesis induced by pravastatin is not overcome by zeatin or a cytokinin-like compound, whereas the inhibition of alkaloid accumulation can be partially overcome. The use of pravastatin shows that the availability of mevalonate for primary and secondary metabolism is differently regulated in Catharanthus roseus cells.     

Autoregulation by the juxtamembrane region of the human ephrin receptor tyrosine kinase A3 (EphA3)

Ephrin receptors (Eph) affect cell shape and movement, unlike other receptor tyrosine kinases that directly affect proliferative pathways. The kinase domain of EphA3 is activated by ephrin binding and receptor oligomerization. This activation is associated with two tyrosines in the juxtamembrane region; these tyrosines are sites of autophosphorylation and interact with the active site of the kinase to modulate activity. This allosteric event has important implications both in terms of understanding signal transduction pathways mediated by Eph kinases as well as discovering specific therapeutic ligands for receptor kinases. In order to provide further details of the molecular mechanism through which the unphosphorylated juxtamembrane region blocks catalysis, we studied wild-type and site-specific mutants in detail. High-resolution structures of multiple states of EphA3 kinase with and without the juxtamembrane segment allowed us to map the coupled pathway of residues that connect the juxtamembrane segment, the activation loop, and the catalytic residues of the kinase domain. This highly conserved set of residues likely delineates a molecular recognition pathway for most of the Eph RTKs, helping to characterize the dynamic nature of these physiologically important enzymes.     

Allophycocyanin: trimers,monomers, subunits,and homodimers

Allophycocyanin is a photosynthetic light-harvesting pigment-protein complex located in the phycobilisomes of cyanobacteria and red algae. Using dynamic light scattering and circular dichroism, solutions of purified allophycocyanin were shown to consist of homogeneous trimers (alpha3beta3) with a nonspherical shape over a very wide range of protein concentrations at pH 6.0 and 20 degrees C. Deconvolutions of the visible circular dichroism spectrum of the trimer were carried out for the first determination of the individual spectra of all six-component chromophores. The chromophores were shown to be in different microenvironments that helped determine the spectrum of the trimer. Monomers (alpha beta) that were formed in either the presence of 0.50M NaSCN or at 45 degrees C were shown to be completely reversible to trimers. However, subunits (alpha and beta) that were formed in either the presence of 8M urea or at 60 degrees C, using spectroscopy and gel-filtration column chromatography, were observed to only partially reconstitute trimers. Homodimers (alpha2 and/or beta2) formed during the regeneration of trimers. The homodimer, which was detected for the first time when both subunits were present, was shown to be in equilibrium with its subunits. Unlike the trimer situation, subunits were found to fully reconstitute monomers in the presence of 0.50M NaSCN. These results suggest a route to trimer assembly from subunits with monomers serving as intermediaries and the homodimers forming in a nonproductive step that did not interfere with the overall assembly scheme.     

Bayesian estimation of dominance merits in noninbred populations by using Gibbs sampling with two reduced sets of mixed model equations

Henderson's mixed model equations system is generally required in a Gibbs sampling application. In two previous studies, we proposed two indirect solving approaches that give dominance values in an animal model context with no need to process all this system. The first one does not require D-1 and the second is based on processing the additive animal model residuals. In the present work, we show that these two methods can be handled iteratively. Since the Bayesian approach is now a widely used tool in estimation of genetic parameters, the main part of this work is devoted to a Gibbs sampling application that can be accelerated by means of the aforementioned indirect solving methods. Three replicates of a population data set are simulated in the paper to compare the applications and estimates. This shows effectively that the estimates given by implementing a Gibbs sampler with each of the two suggested solving methods are obtained with less computational time and are comparable to those given by considering the integral system, particularly when priors are more weighted.     

Yeast strains from the endogenous microflora of the olive fliesBactrocera oleae larvae which could degrade the olive oil mill wastewaters polyphenols

Worldwide, wastewaters constitute a major environmental pollutant. They are very toxic against a wide range of plants and soil microorganisms. Their toxicity is due to the presence of compounds such as polyphenols. In this study, we have isolated yeast strains from the endogenous microflora of the olive fliesBactrocera oleae larvae that were capable of degrading the olive oil mill wastewater polyphenols. The results obtained showed the presence, in the digestive tract of the larvae, of yeast strains resisting to polyphenols. Two resistant strains were isolated and have shown variable capacity of polyphenols degradation that could reach up to 72%. The two isolated strains were identified by two methods: conventional technique and molecular method associating PCR amplification and DNA sequencing of the 5.8S ribosomal RNA gene. Both techniques showed that the two isolated strains corresponded to theCandida diddensiae specie. Related to its capacity to degrade polyphenols, this specie would be a potential candidate for wastewater treatment and environmental protection.     

Structural basis of allele variation of human thiopurine-S-methyltransferase

Human thiopurine S-methyltransferase (TPMT) exhibits considerable person-to-person variation in activity to thiopurine drugs. We have produced an N-terminal truncation of human TPMT protein, crystallized the protein in complex with the methyl donor product S-adenosyl-L-homocysteine, and determined the atomic structure to the resolution of 1.58 and 1.89 A, respectively, for the seleno-methionine incorporated and wild type proteins. The structure of TPMT indicates that the naturally occurring amino acid polymorphisms scatter throughout the structure, and that the amino acids whose alteration have the most influence on function are those that form intra-molecular stabilizing interactions (mainly van der Waals contacts). Furthermore, we have produced four TPMT mutant proteins containing variant alleles of TPMT*2, *3A, *3B, and *3C and examined the structure-function relationship of the mutant proteins based on their expression and solubility in bacteria and their thermostability profile.