Mechanism of the citrate transporters in carbohydrate and citrate cometabolism in Lactococcus and Leuconostoc species

Citrate metabolism in the lactic acid bacterium Leuconostoc mesenteroides generates an electrochemical proton gradient across the membrane by a secondary mechanism (C. Marty-Teysset, C. Posthuma, J. S. Lolkema, P. Schmitt, C. Divies, and W. N. Konings, J. Bacteriol. 178:2178-2185, 1996). Reports on the energetics of citrate metabolism in the related organism Lactococcus lactis are contradictory, and this study was performed to clarify this issue. Cloning of the membrane potential-generating citrate transporter (CitP) of Leuconostoc mesenteroides revealed an amino acid sequence that is almost identical to the known sequence of the CitP of Lactococcus lactis. The cloned gene was expressed in a Lactococcus lactis Cit- strain, and the gene product was functionally characterized in membrane vesicles. Uptake of citrate was counteracted by the membrane potential, and the transporter efficiently catalyzed heterologous citrate-lactate exchange. These properties are essential for generation of a membrane potential under physiological conditions and show that the Leuconostoc CitP retains its properties when it is embedded in the cytoplasmic membrane of Lactococcus lactis. Furthermore, using the same criteria and experimental approach, we demonstrated that the endogenous CitP of Lactococcus lactis has the same properties, showing that the few differences in the amino acid sequences of the CitPs of members of the two genera do not result in different catalytic mechanisms. The results strongly suggest that the energetics of citrate degradation in Lactococcus lactis and Leuconostoc mesenteroides are the same; i.e., citrate metabolism in Lactococcus lactis is a proton motive force-generating process.     

Munich dark matter search

We plan a dark matter search using cryogenic calorimetric detectors with superconducting phase transition thermometers. We discuss such an experiment, compare its estimated sensitivity range with other dark matter searches, and discuss its planned realization.     

Glutathione peroxidase-like activity of simple selenium compounds. Peroxides and the heterocyclic N-oxide resazurin acting as O-atom donors

Selenite and selenocystamine [(CyaSe)2] efficiently activate the decomposition of H2O2 by GSH and by other thiols, as demonstrated using a leuco crystal violet POD-based H2O2 assay which is applicable (unlike other assays) also in presence of thiols. The GPx-like activities were estimated to be 3.6 and 2.7 mumol H2O2/min per mumol SeO3(2-) and (CyaSe)2, respectively. Both selenium compounds also activate reduction of the heterocyclic N-oxide resazurin (RN-->O) to resorufin (RN) by GSH; H2O2 competes with reduction of this dye. GSSeH and CyaSeH, formed by interaction of GSH with SeO3(2-) and (CyaSe)2, respectively, are likely to be the active reductants. CyaSeH, generated gamma-radiolytically from (CyaSe)2, exhibits an absorption peak at 243 nm and is removed by H2O2 with a rate constant of 9.7 x 10(2) M-1 s-1, and slightly slower by hydroperoxides. We have no evidence for one-electron interactions between GSSeH or CyaSeH and H2O2, with formation of free radical intermediates, as previously proposed in the case of selenium-activated reduction of cytochrome c by GSH (Levander et al., Biochemistry 23, 4591-4595 (1973)). Our results can be explained by O-atom transfer from the substrate to the active selenol group, RSeH + H2O2 (RN-->O)-->RSeOH + H2O (RN), and recycling of RSeOH to RSeH (+ H2O) by GSH, analogous to the selenenic acid pathway of GPx. The substrate specificity appears to be different, however, in that GPx is unable to catalyse RN-->O reduction, and GSSeH hardly catalyses the decomposition of cumene- or t-butyl-hydroperoxide; CyaSeH, on the other hand, is active also with the hydroperoxides. RN-->O is reduced to RN also by certain oxidizing free radicals, e.g. by the thiyl CyaS.., O-atom transfer may in this case lead to the generation of reactive oxyl radicals.     

Generation of isothermal spreading data and interfacial energy data for liquid reactive metals on ceramic substrates: The copper-titanium/alumina system

The sessile drop technique is frequently used to evaluate the wettability and spreadability of liquid metals on ceramic substrates. In this study, the spreading kinetics of copper-20 wt% titanium alloys on polycrystalline alumina were evaluated based on measurements of spreading radius versus time. The process of spreading was monitored by anin situ video recording system. The tests were performed using three different initial metal configurations. It was found that conventional sessile drop testing configurations cannot be used to generate isothermal spreading kinetics data because of significant spreading during the heat-up cycle from the solidus temperature to the test temperature. An improved sessile drop technique was developed which eliminated the non-isothermal experience by introducing the liquid copper to the solid titanium/alumina at the desired testing temperature. Using this technique, only a few seconds of data were lost (while the liquid copper dissolved the solid titanium). Because very limited interfacial energy data exist for the copper-titanium/alumina system, especially at higher titanium concentrations, the equilibrium contact angle, the solid-liquid interfacial energy, and the work of adhesion from 1000 to 1300 °C are also presented.     

Channel-forming leucotoxins from Staphylococcus aureus cause severe inflammatory reactions in a rabbit eye model

Seven families, multiply affected by bipolar mood disorder, have been collected from the Irish population and have been genotyped with microsatellite markers from the pericentromeric region of chromosome 18, a region that has been implicated as a site for a susceptibility gene for this relative common psychiatric disorder. The families significantly excluded linkage of bipolar disorder to this region under various models. Although the data provided no evidence of linkage heterogeneity among families, the number of families investigated may be too small to exclude completely the possibility of linkage in a small number of families.     

Heuristic and exact algorithms for the multi-pile vehicle routing problem

The multi-pile vehicle routing problem is a particular combination of loading and routing problems, in which items have to be loaded into different piles within vehicles, and then delivered with minimum cost. The problem is motivated by a real-world timber distribution problem, and is of both theoretical and practical interest. In this paper, we first develop heuristic and exact methods to solve the loading problem. We then include these methods into a tailored combination of Variable Neighborhood Search and Branch-and-Cut, to solve the overall problem. Extensive computational results show how the resulting algorithms are capable of solving to optimality a large number of small-size instances, and of consistently outperforming previous algorithms from the literature on large-size and real-world instances.     

Suspended and localized single nanostructure growth across a nanogap by an electric field

Direct growth of a suspended single nanostructure (SSN) at a specific location is presented. The SSN is grown across a metallic nanoscale gap by migration in air at room temperature. The nanogap is fabricated by industrial standard optical lithography and anisotropic wet chemical silicon etching. A DC current bias, 1 nA, is applied across the metallic gap to induce nanoscale migration of Zn or ZnO. The history of the voltage drop across the gap as a function of time clearly indicates the moment when migration begins. The shape of SSNs grown across the nanogap by the migration is asymmetric at each electrode due to the asymmetric electric field distribution within the nanogap. An SSN can be used as the platform for two-terminal active or passive nanoscale electronics in optoelectronics, radio frequency (RF) resonators, and chemical/biological sensors.