Dialkyl phosphate-related ionic liquids as selective solvents for xylan

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.     

Translational control by cytoplasmic polyadenylation in Xenopus oocytes

Elongation of the poly(A) tails of specific mRNAs in the cytoplasm is a crucial regulatory step in oogenesis and early development of many animal species. The best studied example is the regulation of translation by cytoplasmic polyadenylation elements (CPEs) in the 3' untranslated region of mRNAs involved in Xenopus oocyte maturation. In this review we discuss the mechanism of translational control by the CPE binding protein (CPEB) in Xenopus oocytes as follows: Finally we discuss some of the remaining questions regarding the mechanisms of translational regulation by cytoplasmic polyadenylation and give our view on where our knowledge is likely to be expanded in the near future.     

Spatial and temporal variability of saphrophytic bacteria in the surface waters of Paranaguá and Antonina Bays,Paraná, Brazil

Spatial and temporal variability in the concentration of saprophytic bacteria was investigated in surface waters of Paranaguá and Antonina bays.Seven points along a profile from the entrance of Paranaguá Bay to the innermost part of Antonina Bay, were sampled monthly from November 1985 to November 1986. Temperature, dissolved oxygen, pH and precipitation data were also measured.ZoBell 2216E culture medium was utilized with freshwater and 32% salinity water.Principal component analysis of biotic and abiotic data showed a gradient from the innermost bay to the baymouth bar with an increase in bacteria concentration at Antonina Bay. Significant variation was not observed among sampling stations at Paranaguá Bay, except for February 1986 when there was a homogeneous increase of bacteria throughout both bays in association with an increase in temperature and precipitation. There was also no strong variation of saprophyte numbers at sampling locations near Paranaguá city, despite domestic and harbour waste input.We conclude that the outer region of the estuary is highly influenced by the adjacent ocean and that the inner part has typical estuarine characteristics. The region may be considered little polluted.     

Whole plant aspects of heavy metal induced changes in CO2, uptake and water relations of spruce (Picea abies) seedlings

Spruce seedlings [ Picea abies (L.) Karst.] were exposed to a range of concentrations of Zn, Cd, Hg and methyl-Hg for 5 weeks. The chlorophyll and water content of the needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plant were determined using a Li-cor portable photosynthesis measuring system. Chlorophyll and water contents of needles decreased in response to all metal treatments, as did CO₂ uptake. At 1 μ M Cd, 0.1 μ M Hg and 30 and 60 μ M Zn, the decrease in CO₂ uptake could be accounted for by decreased chlorophyll concentrations. Decreased transpiration was only found at 5 μ M Cd and 0.01 μ M methyl-Hg. At 5 μ M Cd most of the decrease in CO₂ uptake could be explained by decreased chlorophyll levels and stomatal closure induced by water stress. At 0.01 μ M methyl-Hg, besides a decrease in chlorophyll concentration and partial stomatal closure, photosynthetic reactions may have been directly affected. Respiration rates were not influenced by exposure to heavy metals.     

Ribosomes stalling on uORF1 in the Xenopus Cx41 5' UTR inhibit downstream translation initiation

Translation of Xenopus laevis Connexin41 mRNA is strongly controlled by the three upstream open reading frames (uORFs) in its 5′ untranslated region. Mutation of uAUG1 into AAG induced a 100-fold increase in translation of a green fluorescent protein (GFP) reporter ORF. The termination codon of uORF1 was mutated and the uORF was linked in-frame with the GFP ORF, enabling visualisation of initiation at uAUG1 by synthesis of an elongated GFP form. Unexpectedly, hardly any elongated GFP was made, suggesting that translation of uORF1 in wild-type mRNA causes constraining of the entry of 40S ribosomal subunits upstream of uORF1. A rare leucine codon, the third codon of uORF1, contributed to the slow translation and thus to slow scanning. Replacement of the rare leucine codon in uORF1 with a common leucine codon stimulated GFP translation. Remarkably, the rare leucine codon, the termination codon of uORF1, uAUG2 and uAUG3 all improved recognition of uAUG1. Apparently, the block formed by a stalled ribosome on any element in uORF1 prevented the landing of new ribosomal subunits next to the cap and therefore downregulated GFP translation.     

Transformation of some 3α-substituted steroids by Aspergillus tamarii KITA reveals stereochemical restriction of steroid binding orientation in the minor hydroxylation pathway

Aspergillus tamarii contains an endogenous lactonization pathway which can transform progesterone to testololactone in high yield through a sequential four step enzymatic pathway. In this pathway testosterone is formed which primarily undergoes oxidation of the C-17β-alcohol to a C-17 ketone but, can also enter a minor hydroxylation pathway where 11β-hydroxytestosterone is produced. It was recently demonstrated that this hydroxylase could monohydroxylate 3β-hydroxy substituted saturated steroidal lactones in all four possible binding orientations (normal, reverse, inverted normal, inverted reverse) on rings B and C of the steroid nucleus. It was therefore of interest to determine the fate of a series of 3α-substituted steroidal analogues to determine stereochemical effect on transformation. Hydroxylation on the central rings was found to be restricted to the 11β-position (normal binding), indicating that the 3α-stereochemistry removes freedom of binding orientation within the hydroxylase. The only other hydroxylation observed was at the 1β-position. Interestingly the presence of this functional group did not prevent lactonization of the C-17 ketone. In contrast the presence of the 11β-hydroxyl completely inhibited Baeyer–Villiger oxidation, a result which again demonstrates that single functional groups can exert significant control over metabolic handling of steroids in this organism. This may also explain why lactonization of 11β-hydroxytestosterone does not occur. Lactonization of the C-17 ketone was not significantly affected by the 3α-alcohol with significant yields achieved (53%). Interestingly a time course experiment demonstrated that the presence of the 3α-acetate inhibited the Baeyer–Villiger monooxygenase with its activity being observed 24 h later than non-acetate containing analogues. Apart from oxidative transformations observed a minor reductive pathway was revealed with the C-17 ketone being reduced to a C-17β-alcohol for the first time in this organism.     

Reduced expression of SRC family kinases decreases PI3K activity in NBS1-/- lymphoblasts

SRC family kinases (SFKs) are involved in the activation of phosphatidylinositol-3-kinase (PI3K). In addition, the activity of this lipid kinase can be regulated by the DNA repair protein NBS1. Here, we describe a disturbed expression of some members of the non-receptor tyrosine kinase family in lymphoblastoid cell lines generated from cells of Nijmegen breakage syndrome (NBS) patients. Especially, only minor amounts of the kinases LCK and HCK are expressed in the NBS1^−/− cell lines as compared to the consanguineous NBS1^+/− cells. We demonstrate that SFK activity is important for a proper activation of PI3K in these cells and that it is reduced in NBS1^−/− cells. We provide evidence that the observed reduced PI3K activity in NBS lymphoblasts is caused by an impaired expression of the SFKs LCK and/or HCK. Thus, our data establish a new function for the NBS1 protein as a regulator of PI3K activity via SFK members.     

Two parts of the T3S4 domain of the hook-length control protein FliK are essential for the substrate specificity switching of the flagellar type III export apparatus

The switch in export specificity of the type III flagellar protein export apparatus from rod/hook type to filament type is believed to occur upon completion of hook assembly by way of an interaction of the type III secretion substrate specificity switch (T3S4) domain of the hook-length control protein FliK, with the integral membrane export apparatus component FlhB. The T3S4 domain of FliK (FliKT3S4) consisting of amino acid residues 265-405 has an unstable and flexible conformation in its last 35 residues (FliKCT). To investigate the role of FliKT3S4 in substrate specificity switching, we studied the effect of deletions and point mutations within this domain and characterized suppressor mutations. Deletions of ten amino acid residues within the region of residues 301-350 and five amino acids of residues 401-405 abolished switching of export specificity. Site directed mutagenesis showed that highly conserved residues, Val302, Ile304, Leu335, Val401 and Ala405, are essential, and that the five C terminal residues (401-405) are restricted in conformation for the switching process. Suppressor mutant analysis of the fliK(S319Y) mutant, which produces extended hooks with filaments attached due to delayed switching, suggested that FliKT3S4 interacts with the C terminal half of the cytoplasmic domain of FlhB (FlhBC). We propose a two step binding model of FliKT3S4 and FlhBC, in which residues 301-350 of FliK bind to FlhBC upon hook assembly completion at about 55 nm, and then unfolded FliKCT binds to FlhBC to trigger the switch in substrate specificity.