The plastidic pentose phosphate translocator represents a link between the cytosolic and the plastidic pentose phosphate pathways in plants

Plastids are the site of the reductive and the oxidative pentose phosphate pathways, which both generate pentose phosphates as intermediates. A plastidic transporter from Arabidopsis has been identified that is able to transport, in exchange with inorganic phosphate or triose phosphates, xylulose 5-phosphate (Xul-5-P) and, to a lesser extent, also ribulose 5-phosphate, but does not accept ribose 5-phosphate or hexose phosphates as substrates. Under physiological conditions, Xul-5-P would be the preferred substrate. Therefore, the translocator was named Xul-5-P/phosphate translocator (XPT). The XPT shares only approximately 35% to 40% sequence identity with members of both the triose phosphate translocator and the phosphoenolpyruvate/phosphate translocator classes, but a higher identity of approximately 50% to glucose 6-phosphate/phosphate translocators. Therefore, it represents a fourth group of plastidic phosphate translocators. Database analysis revealed that plant cells contain, in addition to enzymes of the oxidative branch of the oxidative pentose phosphate pathway, ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase in both the cytosol and the plastids, whereas the transketolase and transaldolase converting the produced pentose phosphates to triose phosphates and hexose phosphates are probably solely confined to plastids. It is assumed that the XPT function is to provide the plastidic pentose phosphate pathways with cytosolic carbon skeletons in the form of Xul-5-P, especially under conditions of a high demand for intermediates of the cycles.     

Sulfatide is associated with insulin granules and located to microdomains of a cultured beta cell line

Previous studies using pancreas from various mammals and freshly isolated islets from rat pancreas have provided evidence supporting possible involvement of the glycosphingolipid sulfatide in insulin processing and secretion. In this study, sulfatide expression and metabolism in the beta cell line RINr1046-38 (RIN-38), commonly used as a model for beta cell functional studies, were investigated and compared with previous findings from freshly isolated islets. RIN-38 cells expressed similar amounts (2.7 +/- 1.1 nmol/mg protein, n = 19) of sulfatide as isolated rat islets and also followed the same metabolic pathway, mainly through recycling. Moreover, in agreement with findings in isolated islets, the major species of sulfatide isolated from RIN-38 cells contained C16:0 and C24:0 fatty acids. By applying subcellular isolations and electron microscopy and immunocytochemistry techniques, sulfatide was shown to be located to the secretory granules, the plasma membrane and enriched in detergent insoluble microdomains. In the electron microscopy studies, Sulph I staining was also associated with mitochondria and villi structures. In conclusion, RIN-38 cells might be an appropriate model, as a complement to isolated islets where the amount of material often limits the experiments, to further explore the role of sulfatide in insulin secretion and signal transduction of beta cells.     

Role of adipocyte lipid-binding protein (ALBP) and acyl-CoA binding protein (ACBP) in PPAR-mediated transactivation

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that are activated by a number of fatty acids and fatty acid derivatives. By contrast, we have recently shown that acyl-CoA esters display PPAR antagonistic properties in vitro. We have also shown that the adipocyte lipid binding protein (ALBP), the keratinocyte lipid binding protein (KLBP) and the acyl-CoA binding protein (ACBP) exhibit a prominent nuclear localization in differentiating 3T3-L1 adipocytes. Similarly, ectopic expression of these proteins in CV-1 cells resulted in a primarily nuclear localization. We therefore speculated that FABPs and ACBP might regulate the availability of PPAR agonists and antagonists by affecting not only their esterification in the cytoplasm but also their transport to and availability in the nucleus. We show here that coexpression of ALBP or ACBP exerts a negative effect on ligand-dependent PPAR transactivation, when tetradecylthioacetic (TTA) is used as ligand but not when the thiazolidinedione BRL49653 is used as ligand. The results presented here do not support the hypothesis that ALBP facilitates the transport of the fatty acid-type ligands to the nucleus, rather ALBP appears to sequester or increase the turn-over of the agonist. Similarly, our results are in keeping with a model in which ACBP increase the metabolism of these ligands.     

Binding affinity of Escherichia coli RNA polymerase*sigma54 holoenzyme for the glnAp2, nifH and nifL promoters

Escherichia coli RNA polymerase associated with the sigma54 factor (RNAP*sigma54) is a holoenzyme form that transcribes a special class of promoters not recognized by the standard RNA polymerase*sigma70 com plex. Promoters for RNAP*sigma54 vary in their overall 'strength' and show differences in their response to the presence of DNA curvature between enhancer and promoter. In order to examine whether these effects are related to the promoter affinity, we have determined the equilibrium dissociation constant K(d) for the binding of RNAP*sigma54 to the three promoters glnAp2, nifH and nifL. Binding studies were conducted by monitoring the changes in fluorescence anisotropy upon titrating RNAP*sigma54 to carboxyrhodamine-labeled DNA duplexes. For the glnAp2 and nifH promoters similar values of K(d) = 0.94 +/- 0.55 nM and K(d) = 0.85 +/- 0.30 nM were determined at physiological ionic strength, while the nifL promoter displayed a significantly weaker affinity with K(d) = 8.5 +/- 1.9 nM. The logarithmic dependence of K(d) on the ionic strength I was -Deltalog(K(d))/Deltalog(I) = 6.1 +/- 0.5 for the glnAp2, 5.2 +/- 1.2 for the nifH and 2.1 +/- 0.1 for the nifL promoter. This suggests that the polymerase can form fewer ion pairs with the nifL promoter, which would account for its weaker binding affinity.     

Sipaucins A-C,sesquiterpenoids from Siparuna pauciflora

The phytochemical investigation of the leaves of Siparuna pauciflora yielded three novel sesquiterpenoids: the germacrane sipaucin A, the elemane sipaucin B and sipaucin C, comprising a new type of carbon skeleton. In addition, four known aporphine alkaloids-nor-boldine, boldine, laurotetanine, and N-methyl-laurotetanine-were obtained. The evaluation of the antiplasmodial activity of the isolated compounds against two strains of Plasmodium falciparum (PoW, Dd2) showed a moderate activity of nor-boldine.     

Evariquinone,isoemericellin, and stromemycin from a sponge derived strain of the fungus Emericella variecolor

From a strain of the fungus Emericella variecolor derived from the marine sponge Haliclona valliculata, two new natural products, evariquinone and isoemericellin, were isolated after HPLC-UV, -MS, and -NMR studies of the extract and their structures were elucidated by mass spectrometry and NMR experiments. Evariquinone showed antiproliferative activity towards KB and NCI-H460 cells at a concentration of 3.16 microg/ml. Furthermore, the fungus was found to produce the known metabolites stromemycin, shamixanthone, and 7-hydroxyemodin. Chemical degradation, NMR decoupling experiments, and spin-system simulation provided evidence for the double bonds in stromemycin to be all E-configured. ROESY experiments established the monosaccharide moiety to be glucose.