Kinetic pathways of the Nematic-Isotropic phase transition as studied by confocal microscopy on rod-like viruses

We investigate the kinetics of phase separation for a mixture of rodlike viruses (fd) and polymer (dextran), which effectively constitutes a system of attractive rods. This dispersion is quenched from a flow-induced fully nematic state into the region where the nematic and the isotropic phase coexist. We show experimental evidence that the kinetic pathway depends on the overall concentration. When the quench is made at high concentrations, the system is meta-stable and we observe typical nucleation-and-growth. For quenches at low concentration the system is unstable and the system undergoes a spinodal decomposition. At intermediate concentrations we see the transition between both demixing processes, where we locate the spinodal point.Comment: 11 pages, 6 figures, accepted in J. Phys.: Condens. Matter as symposium paper for the 6th Liquid Matter Conference in Utrech

Probing the CP nature of the Higgs boson at linear colliders with tau spin correlations; the case of mixed scalar--pseudoscalar couplings

The prospects for the measurement of the pseudoscalar admixture in the h-tau-tau coupling to a Standard Model Higgs boson of 120 GeV mass are discussed in a quantitative manner e+ e- collisions of 350 GeV centre-of-mass energy. Specific angular distributions in the h --> tau tau; tau --> rho nu decay chain can be used to probe mixing angles of scalar--pseudoscalar h-tau-tau couplings. In the discussion of the feasibility of the method, assumptions on the properties of a future detector for an e+ e- linear collider such as TESLA are used. The Standard Model Higgsstrahlung production process is taken as an example. For the expected performance of a typical Linear Collider set-up, the sensitivity of a measurement of the scalar--pseudoscalar mixing angle turned out to be 6 degree. It will be straightforward to apply our results to estimate the sensitivity of a measurement, in cases another scenario of the Higgs boson sector (Standard Model or not) is chosen by nature. The experimental error of the method is expected to be limited by the statistics.Comment: 10 pages, 7 figures, LaTeX. Corrections of published version include

Nematic-Isotropic Spinodal Decomposition Kinetics of Rod-like Viruses

We investigate spinodal decomposition kinetics of an initially nematic dispersion of rod-like viruses (fd virus). Quench experiments are performed from a flow-stabilized homogeneous nematic state at high shear rate into the two-phase isotropic-nematic coexistence region at zero shear rate. We present experimental evidence that spinodal decomposition is driven by orientational diffusion, in accordance with a very recent theory.Comment: 17 pages, 6 figures, accepted in Phys. Rev.

Brain Aging in the Oldest-Old

Nonagenarians and centenarians represent a quickly growing age group worldwide. In parallel, the prevalence of dementia increases substantially, but how to define dementia in this oldest-old age segment remains unclear. Although the idea that the risk of Alzheimer's disease (AD) decreases after age 90 has now been questioned, the oldest-old still represent a population relatively resistant to degenerative brain processes. Brain aging is characterised by the formation of neurofibrillary tangles (NFTs) and senile plaques (SPs) as well as neuronal and synaptic loss in both cognitively intact individuals and patients with AD. In nondemented cases NFTs are usually restricted to the hippocampal formation, whereas the progressive involvement of the association areas in the temporal neocortex parallels the development of overt clinical signs of dementia. In contrast, there is little correlation between the quantitative distribution of SP and AD severity. The pattern of lesion distribution and neuronal loss changes in extreme aging relative to the younger-old. In contrast to younger cases where dementia is mainly related to severe NFT formation within adjacent components of the medial and inferior aspects of the temporal cortex, oldest-old individuals display a preferential involvement of the anterior part of the CA1 field of the hippocampus whereas the inferior temporal and frontal association areas are relatively spared. This pattern suggests that both the extent of NFT development in the hippocampus as well as a displacement of subregional NFT distribution within the Cornu ammonis (CA) fields may be key determinants of dementia in the very old. Cortical association areas are relatively preserved. The progression of NFT formation across increasing cognitive impairment was significantly slower in nonagenarians and centenarians compared to younger cases in the CA1 field and entorhinal cortex. The total amount of amyloid and the neuronal loss in these regions were also significantly lower than those reported in younger AD cases. Overall, there is evidence that pathological substrates of cognitive deterioration in the oldest-old are different from those observed in the younger-old. Microvascular parameters such as mean capillary diameters may be key factors to consider for the prediction of cognitive decline in the oldest-old. Neuropathological particularities of the oldest-old may be related to “longevity-enabling” genes although little or nothing is known in this promising field of future research

Ontogenic Appearance of MHC Class I (B-F) Antigens During Chicken Embryogenesis

Expression of chicken MHC class (B-F) antigens during ontogeny was determined by binding of anticlass antibody and appearance of B-F transcripts by Northern blotting in chicken organs during embryogenesis until 2 weeks after hatching. MHC class transcripts first become detectable in day 6.5 of embryogenesis. B-F cell-surface expression first becomes detectable in hemopoietic organs by day 10‑12 of embryogenesis and somewhat later in nonhemopoietic organs. Flow cytometry analysis of hemopoietic cells throughout embryogenesis revealed B-Fhi and B-F1 cell populations. The percentage of B-F cells in spleen and bone marrow decreased around hatching, which could reflect either cell flows in these organs during this period or the sensitivity of hemopoietic cells to hatching stress

Degradation of the mycotoxin fusaric acid in burkholderia ambifaria t16: genes and metabolic pathways involved

Fusaric acid (FA, 5-butylpyridine, 2-carboxylic acid) is a secondary metabolite produced by several Fusarium species, which is toxic for bacteria, plants, animals and humans. This mycotoxin contributes to the virulence of phytopathogenic Fusarium in several crops, causing important economic losses. Moreover, FA reduces survival and competition abilities of bacterial species able to antagonize Fusarium spp. due to its negative effects on viability and production of antibiotics effective against these fungi. Burkholderia ambifaria T16 is a bacterial strain isolated from the rhizosphere of barley that showed the interesting ability to degrade FA and detoxify this mycotoxin from barley seedlings. The genes and metabolic pathways involved in FA degradation have not been identified so far in any bacterial species. By screening of a transposon insertion library and proteomic analysis we were able to identify genes and metabolic pathways that would be involved in FA degradation. A functional 2-methylcitrate cycle (2-MCC), a carbon anaplerotic pathway widely distributed among bacteria and fungi where propionyl-CoA is converted to pyruvate and succinate, was shown to be essential for the growth of B. ambifaria T16 in the presence of FA. Propionyl-CoA and its derived catabolites are lethally toxic to cells when accumulate. For that reason, besides providing succinate and pyruvate, the 2-MCC also has a very important role in the detoxification of propionyl-CoA and its catabolites. The comparison of the proteomic profile of B. ambifaria T16 growing with FA or citrate as sole carbon sources showed that more than 50 enzymes were significantly overexpressed during growth with FA, including 2-MCC enzymes and enzymes that convert butyryl-CoA to propanoyl-CoA, suggesting that propanoyl-CoA is produced during FA degradation. Moreover, several proteins, including an AraC-type transcriptional regulator, a FMN-dependent two-component luciferase like monooxygenase (LLM) system, an amidohydrolase, two enoyl-CoA hydratases and a long-chain fatty acid ligase, encoded in the same gene cluster, were highly over-expressed during growth with FA (>10 fold up-regulation). In the last years, two-component LLMs were shown to catalyze the pyridine-ring cleavage of several N-heterocyclic compounds, suggesting that the mentioned gene cluster is a good candidate to be involved in the initial steps of FA degradation in B. ambifaria T16.Fil: Vinacour, Matias Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; ArgentinaFil: Forne, I.. Ludwig Maximilians Universitat; AlemaniaFil: Jung, K.. Ludwig Maximilians Universitat; AlemaniaFil: Imhof, A.. Ludwig Maximilians Universitat; AlemaniaFil: Ruiz, Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; ArgentinaLVII SAIB Meeting; XVI SAMIGE MeetingCiudad Autonoma de Buenos AiresArgentinaSociedad Argentina de Investigación Bioquímica y Biología MolecularSociedad Argentina de Microbiología Genera

The Vibrational Spectrum of the hydrated Alanine-Leucine Peptide in the Amide region from IR experiments and First Principles Calculation

We have combined infrared (IR) experiments with molecular dynamics (MD) simulations in solution at finite temperature to analyse the vibrational signature of the small floppy peptide Alanine-Leucine. IR spectra computed from first- principles MD simulations exhibit no distinct differences between conformational clusters of alpha-helix/beta-sheet-like folds with different orientations of the bulky leucine side chain. All computed spectra show two prominent bands, in good agreement with the experiment, that are assigned to the stretch vibrations of the carbonyl and carboxyl group, respectively. Variations in band widths and exact maxima are likely due to small fluctuations in the backbone torsion angles

Biochemical characterization of the initial steps of the Kennedy pathway in Trypanosoma brucei:the ethanolamine and choline kinases

Note related output below contains correction of this paper.Ethanolamine and choline are major components of the trypanosome membrane phospholipids, in the form of GPEtn (glycero-phosphoethanolamine) and GPCho (glycerophosphocholine). Ethanolamine is also found as an integral component of the GPI (glycosylpliosphatidylinositol) anchor that is required for membrane attachment of cell-surface proteins, most notably the variant-surface glycoproteins. The de novo synthesis of GPEtn and GPCho starts with the generation of phosphoethanolamine and phosphocholine by ethanolamine and choline kinases via the Kennedy pathway. Database mining revealed two putative C/EKs (choline/ethanolamine kinases) in the Trypanosoma brucei genome, which were cloned, overexpressed, purified and characterized. TbEK 1 (T brucei ethanolamine kinase 1) was shown to be catalytically active as an ethanolamine-specific kinase, i.e. it had no choline kinase activity. The K values for ethanolamine and ATP were found to be 18.4 +/- 0.9 and 219 29 mu M respectively. TbC/EK2 (T brucei choline/ethanolamine kinase 2), on the other hand, was found to be able to phosphorylate both ethanolamine and choline, even though choline was the preferred substrate, with a K-m 80 times lower than that of ethanolamine. The K. values for choline, ethanolamine and ATP were 31.4 +/- 2.6 mu M, 2.56 +/- 0.31 mu M and 20.6 +/- 1.96 mu M respectively. Further substrate specificity analysis revealed that both TbEK1 and TbC/EK2 were able to tolerate various modifications at the amino group, with the exception of a quaternary amine for TbEK1 (choline) and a primary amine for TbC/EK2 (ethanolamine). Both enzymes recognized analogues with substituents oil C-2, but substitutions oil C-1 and elongations of the carbon chain were not well tolerated.Publisher PDFPeer reviewe

The importance of early arthroscopy in athletes with painful cartilage lesions of the ankle: a prospective study of 61 consecutive cases

BACKGROUND Ankle sprains are common in sports and can sometimes result in a persistent pain condition. PURPOSE Primarily to evaluate clinical symptoms, signs, diagnostics and outcomes of surgery for symptomatic chondral injuries of the talo crural joint in athletes. Secondly, in applicable cases, to evaluate the accuracy of MRI in detecting these injuries. Type of study: Prospective consecutive series. METHODS Over around 4 years we studied 61 consecutive athletes with symptomatic chondral lesions to the talocrural joint causing persistent exertion ankle pain. RESULTS 43% were professional full time athletes and 67% were semi-professional, elite or amateur athletes, main sports being soccer (49%) and rugby (14%). The main subjective complaint was exertion ankle pain (93%). Effusion (75%) and joint line tenderness on palpation (92%) were the most common clinical findings. The duration from injury to arthroscopy for 58/61 cases was 7 months (5.7–7.9). 3/61 cases were referred within 3 weeks from injury. There were in total 75 cartilage lesions. Of these, 52 were located on the Talus dome, 17 on the medial malleolus and 6 on the Tibia plafond. Of the Talus dome injuries 18 were anteromedial, 14 anterolateral, 9 posteromedial, 3 posterolateral and 8 affecting mid talus. 50% were grade 4 lesions, 13.3% grade 3, 16.7% grade 2 and 20% grade 1. MRI had been performed pre operatively in 26/61 (39%) and 59% of these had been interpreted as normal. Detection rate of cartilage lesions was only 19%, but subchondral oedema was present in 55%. At clinical follow up average 24 months after surgery (10–48 months), 73% were playing at pre-injury level. The average return to that level of sports after surgery was 16 weeks (3–32 weeks). However 43% still suffered minor symptoms. CONCLUSION Arthroscopy should be considered early when an athlete presents with exertion ankle pain, effusion and joint line tenderness on palpation after a previous sprain. Conventional MRI is not reliable for detecting isolated cartilage lesions, but the presence of subchondral oedema should raise such suspicion