Hexagonal silicon-germanium nanowire branches with tunable composition.

Hexagonal SiGe-2H has been recently shown to have a direct bandgap, and holds the promise to be compatible with silicon technology. Hexagonal Si and Ge have been grown on an epitaxial lattice matched template consisting of wurtzite GaP and GaAs, respectively. Here, we present the growth of hexagonal Si and SiGe nanowire branches grown from a wurtzite stem by the vapor-liquid-solid growth mode, which is substantiated byin situtransmission electron microscopy. We show that the composition can be tuned through the whole range of stoichiometry from Si to Ge, and the possibility to realize Si and SiGe heterostructures in these branches.

Cracking the Si Shell Growth in Hexagonal GaP-Si Core-Shell Nanowires.

Semiconductor nanowires have increased the palette of possible heterostructures thanks to their more effective strain relaxation. Among these, core-shell heterostructures are much more sensitive to strain than axial ones. It is now accepted that the formation of misfit dislocations depends both on the lattice mismatch and relative dimensions of the core and the shell. Here, we show for the first time the existence of a new kind of defect in core-shell nanowires: cracks. These defects do not originate from a lattice mismatch (we demonstrate their appearance in an essentially zero-mismatch system) but from the thermal history during the growth of the nanowires. Crack defects lead to the development of secondary defects, such as type-I1 stacking faults and Frank-type dislocations. These results provide crucial information with important implications for the optimized synthesis of nanowire-based core-shell heterostructures.

Characterization, expression and functional aspects of a novel protein tyrosine phosphatase epsilon isoform.

This report describes the identification and characterization of a novel cytoplasmic isoform of human protein tyrosine phosphatase epsilon (PTPepsilon). The novel isoform, denoted cyt-PTPepsilonPD1, displays only the N-terminal catalytic, active phosphatase domain 1 (PD1) which is common in all known PTPepsilon isoforms. In addition, it contains a unique 132-residue long C-terminal end with no known motifs or homology to other characterized proteins. RNAse protection assay on isolated leucocyte subpopulations and selected cell lines demonstrated highest expression of cyt-PTPepsilonPD1 in monocytes. The mRNA-encoding cyt-PTPepsilonPD1 is detected as distinct transcript(s) by Northern blot analysis and is a result of alternative splicing. cyt-PTPepsilonPD1 shows similar cellular localization in transfected cells, both in the cytoplasm and nucleus, as has been previously described for cytoplasmic PTPepsilon isoform. Our previous data suggest that the expression of cytoplasmic PTPepsilon inhibits the mitogen-activated protein kinase cascade through the extracellular signal-regulated kinase 1 and 2 pathway. A similar functional role is also presented here for cyt-PTPepsilonPD1, supporting our previous data suggesting that the catalytic first PD of PTPepsilon is responsible for this inhibition.

Expression of human protein tyrosine phosphatase epsilon in leucocytes: a potential ERK pathway-regulating phosphatase.

The expression of protein tyrosine phosphatase epsilon (PTPepsilon) was studied in human tissues and blood cells. High mRNA expression was observed in peripheral blood leucocytes, particularly in monocytes and granulocytes which revealed at least four distinct transcripts. In lymphocytes, PTPepsilon expression was induced after 12-O-tetradecanoylphorbol-13-acetate (TPA) or antigen-receptor stimulation, indicating that PTPepsilon plays a role in the events taking place after antigen engagement. Previously, PTPepsilon has been shown to be involved in regulating voltage-gated potassium channel activity, insulin-receptor signalling and Janus kinase-signal transducers and activators of transcription (STAT) signalling. Transfection of cells with different PTPepsilon constructs and activator protein-1 reporter gene indicates that the catalytic activity of PTPepsilon is involved in the regulation of the mitogen-activated protein kinase cascade. In particular, the extracellular signal-regulated kinases (ERK1/2) were shown to be inhibited in both phosphorylation status and enzymatic activity after overexpression of PTPepsilon. Thus, PTPepsilon emerges as a phosphatase with a potential to regulate the ERK1/2 pathway either directly or indirectly through its catalytic activity.

A signal sequence trap based on cell enrichment using anti-CD19 antibody coated magnetic beads.

Precursors of many secreted and cell surface proteins contain NH2-terminal signal sequences that lead proteins into the endoplasmic reticulum and to the cell surface. Methods have been developed to clone and identify such proteins by trapping their NH2-terminal signal sequences, so called signal sequence traps. In this study we present an alternative and simplified signal sequence trap based on the combination of a novel vector construct expressing a cDNA library in fusion with a CD19 reporter gene, transfection in mammalian cells and selection of cells expressing trapped signal sequences using magnetic beads. Using this method we have isolated several known and novel factors with signal peptides.

Biological and molecular characterization of a two-peptide lantibiotic produced by Lactococcus lactis IFPL105.

The lactic acid bacterium Lactococcus lactis IFPL105 secretes a broad spectrum bacteriocin produced from the 46 kb plasmid pBAC105. The bacteriocin was purified to homogeneity by ionic and hydrophobic exchange and reverse-phase chromatography. Bacteriocin activity required the complementary action of two distinct peptides (alpha and beta) with average molecular masses of 3322 and 2848 Da, respectively. The genes encoding the two peptides were cloned and sequenced and were found to be identical to the ltnAB genes from plasmid pMRC01 of L. lactis DPC3147. LtnA and LtnB contain putative leader peptide sequences similar to the known 'double glycine' type. The predicted amino acid sequence of mature LtnA and LtnB differed from the amino acid content determined for the purified alpha and beta peptides in the residues serine, threonine, cysteine and alanine. Post-translational modification, and the formation of lanthionine or methyllanthionine rings, could partly explain the difference. Hybridization experiments showed that the organization of the gene cluster in pBAC105 responsible for the production of the bacteriocin is similar to that in pMRC01, which involves genes encoding modifying enzymes for lantibiotic biosynthesis and dual-function transporters. In both cases, the gene clusters are flanked by IS946 elements, suggesting an en bloc transposition. The findings from the isolation and molecular characterization of the bacteriocin provide evidence for the lantibiotic nature of the two peptides.

Complementary and overlapping selectivity of the two-peptide bacteriocins plantaricin EF and JK.

Plantaricin EF and JK are both two-peptide bacteriocins produced by Lactobacillus plantarum C11. The mechanism of plantaricin EF and JK action was studied on L. plantarum 965 cells. Both plantaricins form pores in the membranes of target cells and dissipate the transmembrane electrical potential (Deltapsi) and pH gradient (DeltapH). The plantaricin EF pores efficiently conduct small monovalent cations, but conductivity for anions is low or absent. Plantaricin JK pores show high conductivity for specific anions but low conductivity for cations. These data indicate that L. plantarum C11 produces bacteriocins with complementary ion selectivity, thereby ensuring efficient killing of target bacteria.

Membrane-mimicking entities induce structuring of the two-peptide bacteriocins plantaricin E/F and plantaricin J/K.

Lactobacillus plantarum C11 produces plantaricin E/F (PlnE/F) and plantaricin J/K (PlnJ/K), two bacteriocins whose activity depends on the complementary action of two peptides (PlnE and PlnF; PlnJ and PlnK). Three of the individual Pln peptides possess some antimicrobial activity, but the highest bacteriocin activity is obtained by combining complementary peptides in about a one-to-one ratio. Circular dichroism was used to study the structure of the Pln peptides under various conditions. All four peptides were unstructured under aqueous conditions but adopted a partly alpha-helical structure in the presence of trifluoroethanol, micelles of dodecylphosphocholine, and negatively charged dioleoylphosphoglycerol (DOPG) liposomes. Far less structure was induced by zwitterionic dioleoylglycerophosphocholine liposomes, indicating that a net negative charge on the phospholipid bilayer is important for a structure-inducing interaction between (positively charged) Pln peptides and a membrane. The structuring of complementary peptides was considerably enhanced when both (PlnE and PlnF or PlnJ and PlnK) were added simultaneously to DOPG liposomes. Such additional structuring was not observed in experiments with trifluoroethanol or dodecylphosphocholine, indicating that the apparent structure-inducing interaction between complementary Pln peptides requires the presence of a phospholipid bilayer. The amino acid sequences of the Pln peptides are such that the alpha-helical structures adopted upon interaction with the membrane and each other are amphiphilic in nature, thus enabling membrane interactions.

Plantaricin A is an amphiphilic alpha-helical bacteriocin-like pheromone which exerts antimicrobial and pheromone activities through different mechanisms.

Production of bacteriocins by lactic acid bacteria is in some cases regulated by a quorum sensing mechanism that involves a secreted bacteriocin-like peptide pheromone. In the case of Lactobacillus plantarum C11, this pheromone, the 26-mer plantaricin A (PlnA), has the interesting property of having both bacteriocin and pheromone activities. To gain insight into how PlnA functions as a pheromone and as a bacteriocin, the L- and D-enantiomers of an N-terminally truncated form of PlnA were synthesized (PlnA-22L and PlnA-22D; PlnA-22L has full biological activity). With circular dichroism, it was shown that the two peptides are unstructured in aqueous solution, but they adopt mirror-image amphiphilic helical structures in the presence of trifluoroethanol and membrane-mimicking entities such as micelles of dodecylphosphocholine and negatively charged Ole2GroPGro liposomes, but not in the presence of zwitterionic Ole2GroPCho liposomes. Thus, the negative charge on the membrane is important for structuring of the (positively charged) PlnA peptides. In terms of in vivo antimicrobial activity, PlnA-22L and PlnA-22D behaved almost identically. Likewise, the peptides dissipated the membrane potential and the transmembrane pH gradient in sensitive cells equally effectively. PlnA-22L induced bacteriocin production in L. plantarum C11 (i.e., displayed pheromone activity), the level of induction being clearly dose-dependent. PlnA-22D did not display pheromone activity, but, at high concentrations, was able to inhibit the pheromone activity of PlnA-22L. The results indicate that the antimicrobial activity of PlnA does not require chiral interactions and is mediated through the formation of a strongly amphiphilic alpha-helical structure. In contrast, PlnA's pheromone activity is dependent on a chiral interaction between the amphiphilic helix (PlnA-22L) and a receptor protein. One may speculate that PlnA is an evolutionary intermediate between a true bacteriocin and a pheromone.

Amphiphilic alpha-helices are important structural motifs in the alpha and beta peptides that constitute the bacteriocin lactococcin G--enhancement of helix formation upon alpha-beta interaction.

Lactococcin G (LcnG) is an antimicrobial substance (bacteriocin) consisting of two peptides, LcnG-alpha and LcnG-beta. The structures of intact LcnG-alpha and LcnG-beta as well as various fragments of these peptides were studied by circular dichroism (CD) under several conditions. All peptides had a non-structured conformation in aqueous solutions. In the presence of trifluoroethanol, dodecylphosphocholine micelles and (negatively charged) dioleoylglycerophosphoglycerol (Ole2GroPGro) liposomes, varying amounts of alpha-helical structure were induced. Comparisons of the various fragments showed that helicity was concentrated in those parts of LcnG-alpha and LcnG-beta that would become amphiphilic if an alpha-helical structure was adopted. In the presence of zwitterionic dioleoylglycerophosphocholine (Ole2GroPCho) liposomes, the peptides were much less (if at all) structured, suggesting that the excess of positive charge on the antimicrobial peptides needs to be compensated by an excess of negative charge on the membrane. The structuring of LcnG-alpha and LcnG-beta in the presence of Ole2GroPGro liposomes was considerably enhanced when both peptides were presented simultaneously to the membranes. Consecutive addition of the two peptides to Ole2GroPGro liposomes did not give this additional structuring, indicating that the individual LcnG-alpha and LcnG-beta peptides associate with the membrane in a virtually irreversible manner that makes them inaccessible for interaction with the complementary peptide. The results suggest that upon arrival at and interaction with the target membrane, LcnG-alpha and LcnG-beta form a complex that consists of approximately 50% amphiphilic alpha-helices.

Mechanistic properties of the two-component bacteriocin lactococcin G.

Lactococcin G is a bacteriocin whose activity depends on the complementary action of two peptides, termed alpha and beta. Biologically active, synthetic lactococcin G was used to study the mode of action on sensitive cells of Lactococcus lactis. The alpha and beta peptides can bind independently to the target cell surface, but activity requires the complementary peptide. Once bound to the cell surface, the peptides cannot be displaced to the surfaces of other cells. A complex of alpha and beta peptides forms a transmembrane pore that conducts monovalent cations but not protons. Efflux of potassium ions is observed only above pH 5.0, and the rate of efflux increases steeply with the pH. The consequences of cation fluxes for the viability of the target cells are discussed.

Can training improve the results with infrared tympanic thermometers?

BACKGROUND: Infrared tympanic thermometry (ITT) is a method for body temperature measurement. Correct measuring technique is said to be important to achieve good results with this method. The objective of this study was to investigate the accuracy and effect of training in the use of infrared tympanic thermometry (ITT) on the measurement results. METHOD: Nurses trained in the use of ITT, and nurses not trained performed measurement sequences on 65 patients: one rectal and two ITT measurements in each sequence. RESULTS: Mean rectal temperatures were significantly (P < 0.01) higher than with ITT (0.44 +/- 0.42 (SD) degree C for trained, 0.56 +/- 0.4 (SD) degree C for untrained). Coefficient of repeatability for ITT measurements was +/- 0.54 degree C for trained nurses, and +/- 0.48 degree C for untrained. With ITT temperatures adjusted upwards of 0.5 degree C, the sensitivity of ITT for detecting fever as defined by rectal measurements would be 70% for trained, and 54% for untrained nurses. Repeatability and sensitivity for trained and untrained nurses were not significantly (P > 0.05) different. CONCLUSION: Training had little effect on the accuracy of the measurements. According to our results, ITT is often unreliable and should be used with caution.

[Waiting lists guarantee in health care. Some theoretical reflections]. / Ventelistegaranti og køer i helsevesenet. Noen teoretiske refleksjoner.

In 1990 a "waiting list guarantee" was introduced in the Norwegian health care system to secure treatment within six months for patients belonging to priority group II. (Priority group II are patients in need of treatment to avoid health hazards or serious long-term effects.) This guarantee has been difficult to honour and has caused considerable political unrest in the recent years. In an attempt to reform the guarantee, an analysis of our hospitals' capacity problems has been carried out, based on the general theory of queues. One result was that in order to fulfill the guarantee it is necessary to drastically reduce the queues and increase the capacity to deliver health services. This article presents the reasoning behind the analysis, in order to demonstrate the necessary foundation for a health policy that aims to reduce the time Norwegian patients have to wait for treatment in hospital.

[Infrared tympanic thermometry. Experience and training does not improve the quality of measurement results]. / Infrarød tympanisk termometri. Erfaring og opplaering i bruken av metoden bedrer ikke kvaliteten på målingene.

Nurses, with and without training in the use of infrared tympanic thermometry, performed measurement sequences on patients. One rectal and two repeated measurements with each of two types of equipment for infrared tympanic thermometry (Genius, Core Check) were used in each sequence. Rectal measurements showed temperatures significantly higher than infrared tympanic thermometry, but there were variations (Genius 0.3 +/- 0.58 (SD) degree C, Core Check 0.5 +/- 0.42 (SD) degree C). The sensitivity of infrared tympanic thermometry for fever, as defined by rectal measurements, was 36% for Genius and 21% for Core Check. The quality of the measurements was not improved by training. Our results indicate that infrared tympanic thermometry should be used with caution when screening for fever in hospitals.

Radiotherapy in the treatment of symptomatic vertebral hemangiomas: technical case report.

OBJECTIVE AND IMPORTANCE: In contrast to the frequent finding of vertebral hemangiomas at autopsy and during radiographical examinations, symptomatic lesions are rare. In the literature, a variety of therapies and combinations of therapies have been reported. There is, however, significant inconsistency regarding which therapy is considered appropriate. CLINICAL PRESENTATION: We report a young man with multiple vertebral hemangiomas, epidural extension, and secondary spastic paraparesis. INTERVENTION: Rapid neurological deterioration and the clinical suspicion of malignant disease led to an initial decompressive laminectomy and biopsy of the intraspinal soft tissue lesion. Postoperative radiotherapy produced, however, substantial effects, with complete regression of the epidural hemangioma. CONCLUSION: Based on the literature, we focus on diagnostic problems and choice of therapy for vertebral hemangiomas. Further, we discuss in particular the beneficial role of radiotherapy in the treatment of these nonmalignant lesions.

Lactococcin G is a potassium ion-conducting, two-component bacteriocin.

Lactococcin G is a novel lactococcal bacteriocin whose activity depends on the complementary action of two peptides, termed alpha and beta. Peptide synthesis of the alpha and beta peptides yielded biologically active lactococcin G, which was used in mode-of-action studies on sensitive cells of Lactococcus lactis. Approximately equivalent amounts of both peptides were required for optimal bactericidal effect. No effect was observed with either the alpha or beta peptide in the absence of the complementary peptide. The combination of alpha and beta peptides (lactococcin G) dissipates the membrane potential (delta omega), and as a consequence cells release alpha-aminoisobutyrate, a non-metabolizable alanine analog that is accumulated through a proton motive-force dependent mechanism. In addition, the cellular ATP level is dramatically reduced, which results in a drastic decrease of the ATP-driven glutamate uptake. Lactococcin G does not form a proton-conducting pore, as it has no effect on the transmembrane pH gradient. Dissipation of the membrane potential by uncouplers causes a slow release of potassium (rubidium) ions. However, rapid release of potassium was observed in the presence of lactococcin G. These data suggest that the bactericidal effect of lactococcin G is due to the formation of potassium-selective channels by the alpha and beta peptides in the target bacterial membrane.

Enhancement of iron-catalyzed free radical formation by acidosis in brain homogenates: differences in effect by lactic acid and CO2.

The influence of lactic acidosis and of extreme hypercapnia on free radical generation and lipid peroxidation in brain tissues was studied. Cortical homogenates were prepared from the rat brain in a bicarbonate buffer and incubated for 60 min. Lipid peroxidation was evaluated by measurements of thiobarbituric acid reactive (TBAR) material and alpha-tocopherol analysis. The pH during incubations were decreased to 6.10-6.20 by either lactic acid administration or equilibration with 60% CO2 gas in paired experiments. In homogenates treated with lactic acid there was a 20-fold increase in TBAR material and the alpha-tocopherol concentration decreased to approximately 60% of control. There was only a 10-fold increase in TBAR material and no change in alpha-tocopherol concentration if acidosis was induced by CO2. These differences between lactic acidosis and hypercapnic acidosis were statistically highly significant. The results indicate that lactic acidosis has a more pronounced effect in augmenting free radical generation in brain tissues than acidosis due to an increase in CO2 tension. It is suggested that this effect of lactic acid is mediated by increased dissociation of catalytic iron from proteins of the transferrin type.