DICTYOSTELIUM AUREO-STIPES AND DICTYOSTELIUM TENUE: NEW SPECIES OF THE DICTYOSTELIACEAE

Three new cellular slime molds, Dictyostelium aureo-stipes sp. n., D. aureo-stipes var. helvetium var. n. and D. tenue sp. n., are described which possess characteristics heretofore unrecorded in the Dictyosteliaceae. The two species are unlike in dimensions and complexity of form, yet show a number of features in common, and may in fact be closely related. D. aureo-stipes var. helvetium is relatively large and robust, forming multiple-branched fruiting bodies without the regularity of form found in Polysphondylium, yet tending toward symmetry when well-developed. The golden-yellow stipe is a distinguishing feature of D. aureo-stipes and is even more pronounced in var. helvetium. D. tenue is smaller and simpler in form. The degree of branching is much reduced, and oftentimes a solitary sorus terminates a delicate stipe composed of a single tier of cells. Both species are quite sensitive to environmental conditions, particularly temperature, for optimum development occurs within relatively narrow ranges.     

Trophic interactions in rockpool food webs: regulation of zooplankton and phytoplankton by Notonecta and Daphnia

We studied trophic interactions in experimental rockpools with three different food web structures: phytoplankton and small-bodied zooplankton; phytoplankton, small-bodied zooplankton and Daphnia ; and phytoplankton, small-bodied zooplankton, Daphnia and Notonecta . Nutrients, primary productivity, chlorophyll a and zooplankton species composition and biomass were measured over eight weeks.
2. Daphnia had a negative impact on other zooplankton and reduced the phytoplankton biomass and primary productivity. In the absence of Daphnia , small-bodied zooplankton species were abundant, in particular cyclopoid copepods. Concentrations of dissolved nutrients were lower and the standing crop of primary producers was higher when Daphnia was absent.
3. The presence of the invertebrate predator Notonecta produced a top-down effect which was similar to that reported for planktivorous fish, i.e. a selective reduction of daphnids followed by an increase of small-bodied zooplankton species and phytoplankton biomass.
4. The study showed that consumer regulation of Daphnia by Notonecta and of algae by Daphnia are important, but also demonstrated that trophic level biomasses were controlled by a combination of predation and resource limitation.     

Plasma Glutamine Concentrations in Liver Failure

Background

Higher than normal plasma glutamine concentration at admission to an intensive care unit is associated with an unfavorable outcome. Very high plasma glutamine levels are sometimes seen in both acute and chronic liver failure. We aimed to systematically explore the relation between different types of liver failure and plasma glutamine concentrations.

Methods

Four different groups of patients were studies; chronic liver failure (n = 40), acute on chronic liver failure (n = 20), acute fulminant liver failure (n = 20), and post-hepatectomy liver failure (n = 20). Child-Pugh and Model for End-stage Liver Disease (MELD) scores were assessed as indices of liver function. All groups except the chronic liver failure group were followed longitudinally during hospitalisation. Outcomes were recorded up to 48 months after study inclusion.

Results

All groups had individuals with very high plasma glutamine concentrations. In the total group of patients (n = 100), severity of liver failure correlated significantly with plasma glutamine concentration, but the correlation was not strong.

Conclusion

Liver failure, regardless of severity and course of illness, may be associated with a high plasma glutamine concentration. Further studies are needed to understand whether high glutamine levels should be regarded as a biomarker or as a contributor to symptomatology in liver failure.     

Mitochondrial regulation of cell death: Processing of apoptosis-inducing factor (AIF)

Apoptosis might proceed through the activation of both caspase-dependent and -independent pathways. Apoptosis-inducing factor (AIF) was discovered as the first protein that mediated caspase-independent cell death. Initially, it was regarded as a soluble protein residing in the intermembrane space of mitochondria, from where it could be exported to the nucleus to participate in large-scale DNA fragmentation and chromatin condensation. However, later it was demonstrated that AIF is N-terminally anchored to the inner mitochondrial membrane. Hence, AIF must be liberated from its membrane anchor prior to being released into the cytosol. The current knowledge about the molecular mechanisms regulating the processing and release of AIF from the mitochondria will be summarized and discussed in this review.     

Determination of substrate binding energies in individual subsites of a family 18 chitinase

Thermodynamic parameters for binding of N-acetylglucosamine (GlcNAc) oligomers to a family 18 chitinase, ChiB of Serratia marcescens, have been determined using isothermal titration calorimetry. Binding studies with oligomers of different lengths showed that binding to subsites −2 and +1 is driven by a favorable enthalpy change, while binding to the two other most important subsites, +2 and +3, is driven by entropy with unfavorable enthalpy. These remarkable unfavorable enthalpy changes are most likely due to favorable enzyme-substrate interactions being offset by unfavorable enthalpic effects of the conformational changes that accompany substrate-binding.     

Chemical synthesis of analogs of the glycopeptide contulakin-G, an analgetically active conopeptide from Conus geographus

Cone snails are marine predators that use immobilizing venoms for catching prey. Chemical analysis of the venoms has revealed a variety of biologically active small and intermediate size peptides rich in post-translational modifications (modified amino acids, glycosylation). The glycopeptide contulakin-G (pGlu-Ser-Glu-Glu-Gly-Gly-Ser-Asn-Ala-[beta-D-Galp-(1-->3)-alpha-D-GalpNAc-(1-->]Thr-Lys-Lys-Pro-Tyr-Ile-Leu-OH) is a potent analgesic from Conus geographus venom. The in vivo activity of synthetic contulakin-G was previously found to be significantly higher compared to that of a peptide lacking the glycan. In order to further investigate the importance of the glycan, we have now synthesized analogs of contulakin-G where the glycan chain O-linked to threonine has been altered either to beta-D-Galp-(1-->3)-beta-D-GalpNAc-, alpha-D-Galp-(1-->3)-alpha-D-GalpNAc-, or beta-D-Galp-(1-->6)-alpha-D-GalpNAc-. The glycopeptides were assembled on a Wang resin using commercially available Fmoc amino acids and synthetically prepared Fmoc-protected threonine derivatives carrying O-acetyl protected sugar chains. The final products were thoroughly characterized by NMR and mass spectroscopy.     

Chimeric honeybees (Apis mellifera) produced by transplantation of embryonic cells into pre-gastrula stage embryos and detection of chimerism by use of microsatellite markers

The production of chimeras, by use of cell transplantation, has proved to be highly valuable in studies of development by providing insights into cell fate, differentiation, and developmental potential. So far, chimeric honeybees have been created by nuclear transfer technologies. We have developed protocols to produce chimeric honeybees by use of cell transplantation. Embryonic cells were transplanted between pre-gastrula stage embryos (32-34 hr after oviposition) and hatched larvae were reared in vitro for 4 days. Chimeric individuals were detected by use of microsatellite analysis and a conservative estimation approach. 4.8% of embryos, posteriorly injected with embryonic cells, developed into chimeric honeybee larvae. By injection of cells pre-stained with fluorescent cell tracer dye, we studied the integration of transplanted cells in the developing embryos. Number of injected cells varied from 0 to 50 and cells remained and multiplied mainly in the area of injection.     

Characterization of proton-transporting membranes from resting pig gastric mucosa

Membrane vesicles were purified from resting corpus mucosa of pig stomachs by velocity-sedimentation on a sucrose-Ficoll step gradient. Two vesicular fractions containing the (H+ + K+)-ATPase were obtained. One fraction was tight towards KCl, the other was leaky. At 21 degrees C maximal (H+ + K+)-ATPase activities of 0.8 and 0.4 mumol X mg-1 X min-1, respectively, were observed in lyophilized vesicles. The vesicles contained a membrane-associated carbonic anhydrase, the activity of which was in 100-fold excess of the maximal ATPase activity. Both vesicular fractions were rich in phosphatidylcholine, phosphatidylethanolamine, sphingomyelin and cholesterol. The characteristics of ion permeability and transport in the tight vesicles were in agreement with corresponding data for vesicles of a tubulovesicular origin in the parietal cell. Measurement of the rate of K+ uptake into the vesicles was based on the ability of K+ to promote H+ transport. The uptake was slow and dependent on the type of anion present. The effectiveness in promoting uptake of K+ by anions was SCN- greater than NO3- greater than Cl- much greater than HCO3- greater than SO4(2-). Uptake of K+ was much more rapid at alkaline pH than at neutral or at acidic pH. Addition of CO2 at alkaline pH strongly stimulated the rate of H+ accumulation in the vesicles. The initial part of this stimulation was sensitive to acetazolamide, an inhibitor of carbonic anhydrase. A model how the (H+ + K+)-ATPase and the carbonic anhydrase may co-operate is presented. It is concluded that membrane vesicles of a tubulovesicular origin can produce acid.