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This study presents calcium isotope data for co-existing clinopyroxenes (cpx), orthopyroxenes (opx), and olivine (ol) in mantle xenoliths to investigate Ca isotopic fractionation in the upper mantle. δ 44/40 Ca (δ 44/40 Ca (‰) = ( 44 Ca/ 40 Ca) SAMPLE /( 44 Ca/ 40 Ca) SRM915a − 1) in opx varies from 0.95 ± 0.05‰ to 1.82 ± 0.01‰ and cpx from 0.71 ± 0.06‰ to 1.03 ± 0.12‰ (2se). δ 44/40 Ca in ol (P-15) is 1.16 ± 0.08‰, identical to δ 44/40 Ca of the co-existing opx (1.12 ± 0.09‰, 2se). The Δ 44/40 Ca opx−cpx (Δ 44/40 Ca opx−cpx = δ 44/40 Ca opx –δ 44/40 Ca cpx ) shows a large variation ranging from −0.01‰ to 1.11‰ and it dramatically increases with decreasing of Ca/Mg (atomic ratio) in opx. These observations may reflect the effect of opx composition on the inter-mineral equilibrium fractionation of Ca isotopes, consistent with the theoretical prediction by first-principles theory calculations (Feng et al., 2014). Furthermore, Δ 44/40 Ca opx−cpx decreases when temperature slightly increases from 1196 to 1267 K. However, the magnitude of such inter-mineral isotopic fractionation (1.12‰) is not consistent with the value calculated by the well-known correlation between inter-mineral isotope fractionation factors and 1/ T 2 (Urey, 1947). Instead, it may reflect the temperature control on crystal chemistry of opx (i.e., Ca content), which further affects Δ 44/40 Ca opx−cpx . The calculated δ 44/40 Ca of bulk peridotites and pyroxenites range from 0.76 ± 0.06‰ to 1.04 ± 0.12‰ (2se). Notably, δ 44/40 Ca of bulk peridotites are positively correlated with CaO and negatively with MgO content. Such correlations can be explained by mixing between a fertile mantle end-member and a depleted one with low δ 44/40 Ca, indicating that Ca isotopes could be a useful tool in studying mantle evolution. [ABSTRACT FROM AUTHOR]

Trypanosoma cruzi, the agent of Chagas disease, does not seem to control gene expression through regulation of transcription initiation and makes use of post-transcriptional mechanisms. We report here a 43-nt U-rich RNA element located in the 3'-untranslated region (3'-UTR) of a large number of T. cruzi mRNAs that is important for mRNA abundance in the intracellular amastigote stage of the parasite. Whole genome scan analysis, differential display RT-PCR, Northern blot, and RT-PCR analyses were used to determine the transcript levels of more than 900 U-rich-containing mRNAs of large gene families as well as single and low copy number genes. Our results indicate that the 43-nt U-richmRNAelement is preferentially present in amastigotes. The cis-element of a protein kinase 3'-UTR but not its mutated version promoted the expression of the green fluorescent protein reporter gene in amastigotes. The regulatory ciselement, but not its mutated version, was also shown to interact with the trypanosome-specific RNA-binding protein (RBP) TcUBP1 but not with other related RBPs. Co-immunoprecipitation experiments of TcUBP1-containing ribonucleoprotein complexes formed in vivo validated the interaction with representative endogenous RNAs having the element. These results suggest that this 43-nt U-rich element together with other yet unidentified sequences might be involved in the modulation of abundance and/or translation of subsets of transcripts in the amastigote stage. [ABSTRACT FROM AUTHOR]

Farnesyl-diphosphate synthase (FPPS) catalyzes the synthesis of farnesyl diphosphate, an important precursor of sterols, dolichols, ubiquinones, and prenylated proteins. We report the cloning and characterization of two Toxoplasma gondii famesyl-diphosphate synthase (TgFPPS) homologs. A single genetic locus produces two transcripts, TgFPPS and TgFPPSi, by alternative splicing. Both isoforms were heterologously expressed in Escherichia coli, but only TgFPPS was active. The protein products predicted from the nucleotide sequences have 646 and 605 amino acids and apparent molecular masses of 69.5 and 64.5 kDa, respectively. Several conserved sequence motifs found in other prenyl-diphosphate synthases are present in both TgFPPSs. TgFPPS was also expressed in the baculovirus system and was biochemically characterized. In contrast to the FPPS of other eukaryotic organisms, TgFPPS is bifunetional, catalyzing the formation of both farnesyl diphosphate and geranylgeranyl diphosphate. TgFPPS localizes to the mitochondria, as determined by the co-localisation of the affinity-purified antibodies against the protein with MitoTracker, and in accord with the presence of an N-terminal mitochondria-targeting signal in the protein. This enzyme is an attractive target for drug development, because the order of inhibition of the enzyme by a number of bisphosphonates is the same as that for inhibition of parasite growth. In summary, we report the first bifunctional farnesyl-diphosphate/geranylgeranyldiphosphate synthase identified in eukaryotes, which, together with previous results, establishes this enzyme as a valid target for the chemotherapy of toxoplasmosis. [ABSTRACT FROM AUTHOR]

This study reports Ca-Fe isotope compositions of mineral separates in a set of peridotite xenoliths including ten lherzolites, one harzburgite, and one wehrlite from Hainan Island, south China. Iron isotope compositions show a small variation (<0.15‰ of δ56/54Fe) among olivine (ol), orthopyroxene (opx), and clinopyroxene (cpx). Δ44/40Ca opx-cpx (δ44/40Ca opx -δ44/40Ca cpx) show a large range from 0.00‰ to 1.23‰. Together with data in previous studies, Δ44/40Ca opx-cpx in mantle xenoliths worldwide show a negative correlation with the apparent temperatures, which cannot be explained by equilibrium fractionation. Instead, the observed inter-mineral Ca isotope fractionation between opx and cpx (>2‰) in previous studies should be dominated by disequilibrium sub-solidus Ca redistribution between cpx and opx, which is driven by the changes of mantle temperature and chemical composition in pyroxene. The wehrlite, which was formed by reaction of peridotite with an evolved, silica-undersaturated melt, has δ44/40Ca of 3.22‰ and δ56/54Fe of 0.22‰, significantly heavier than the value of fertile mantle. Such heavy isotope signatures in the wehrlite are best explained by diffusion during the metasomatic melt percolating the refractory mantle. In summary, this study reveals that significant kinetic Ca isotope fractionations could occur in the mantle by inter-mineral Ca diffusion during re-equilibration upon cooling and Ca diffusion from melt into peridotite during melt percolation. [ABSTRACT FROM AUTHOR]

Abstract: A new ligand, pyridine-3,5-bis(benzimidazole-2-yl) (pbb), and four complexes containing pbb, namely [pbb(Hpbb)2]SO4 ·7H2O (1), [Zn(pbb)2(H2O)4](NO3)2 ·2C2H5OH·4H2O (2), [Cd(pbb)2(H2O)4](NO3)2 ·2C2H5OH·4H2O (3) and [Zn2(pbb)2(μ-OH)(μ-OAc)](OAc)2 ·7H2O (4) (HOAc=acetic acid), have been designed, synthesized and characterized. Complexes 1–4 show 3D supramolecular architectures that are connected through hydrogen bonds and aromatic π–π interactions. A self-assembled (H2O)12 cluster with a chair conformation (H2O)6 ring core is observed in 1, which exhibits an unusual association mode of water molecules. Compounds 2 and 3 present 3D supramolecular structures involving 1D open channels encapsulating ions, and crown-like rings are found in 4. In addition, the preliminary antibacterial activity of pbb and its complexes were investigated by two methods, which indicate a selective inhibition property for the tested strains. Strong emissions from the complexes were also changed by the coordination modes in the sold state. [Copyright &y& Elsevier]