195 research outputs found
Stabilisation of Na,K-ATPase structure by the cardiotonic steroid ouabain
Cardiotonic steroids such as ouabain bind with high affinity to the membrane-bound cation-transporting P-type Na,K-ATPase, leading to complete inhibition of the enzyme. Using synchrotron radiation circular dichroism we show that the enzyme-ouabain complex is less susceptible to thermal denaturation (unfolding) than the ouabain-free enzyme, and this protection is observed with Na,K-ATPase purified from pig kidney as well as from shark rectal glands. It is also shown that detergent-solubilised preparations of Na,K-ATPase are stabilised by ouabain, which could account for the successful crystallisation of Na,K-ATPase in the ouabain-bound form. The secondary structure is not significantly affected by the binding of ouabain. Ouabain appears however, to induce a reorganization of the tertiary structure towards a more compact protein structure which is less prone to unfolding; recent crystal structures of the two enzymes are consistent with this interpretation. These circular dichroism spectroscopic studies in solution therefore provide complementary information to that provided by crystallography
Effect of rejection on electrophysiologic function of canine intestinal grafts: Correlation with histopathology and na-k-ATPase activity
To investigate whether electrophysiologic changes can detect the early onset and progress of intestinal rejection, changes in in vitro electrophysiologic function, intestinal histopathology, and Na-K-ATPase activity were studied in dogs. Adult mongrel dogs of both sexes, weighing 18-24 kg, were used for auto and allo small bowel transplantation. The entire small bowels, except for short segments at the proximal and distal ends, were snitched between a pair of dogs (allograft). Animals receiving intestinal autotransplantation were used as controls. AIIograji recipients were sacrificed 3, 4, 5, 7, or 9 days after transplantation, and autograft recipients were sacrificed 3, 7, or 14 days afier transplantation. Immunosuppression was not used. Electrophysiologic measurements were done with an Ussing chamber. Histological analysis was performed blindly using whole thickness sections. Na-K-ATPase activity in the mucosal tissue, which is said to regulate the potential difference, was also measured. Potential difference, resistance, and Na-K-ATPase activity of the allografi intestine decreased with time and were significantly lower 7 and 9 days after transplantation compared to host intestine, normul intestine, and graft intestine of controls (autograft). Potential difference, resistance, and Na-K-ATPase activity of the native intestinal tissue and the autografts did not decrease with time. Detection of histologically mild rejection of the intestine, which is important for appropriate immunosup-pressive treatment in clinical cases, could not be achieved based on electrophysiology or Na-K-ATPase activity. Deterioration of electrophysiologic function during rejection correlated with the histological rejection process and Na-K-ATPase activity; however, electrophysiology my not be a reliable tool for monitoring grafrs, since it cannot detect early intestinal rejection. Š 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
Angle- and polarization-resolved luminescence from suspended and hexagonal boron nitride encapsulated MoSe2 monolayers
The polarized photoluminescence from atomically thin transition metal dichalcogenides is a frequently applied tool to scrutinize optical selection rules and valley physics, yet it is known to sensibly depend on a variety of internal and external material and sample properties. In this work, we apply combined angle- and polarization-resolved spectroscopy to explore the interplay of excitonic physics and phenomena arising from the commonly utilized encapsulation procedure on the optical properties of atomically thinMoSe2.We probe monolayers prepared in both suspended and encapsulated manners.We show that the hBN encapsulation significantly enhances the linear polarization of exciton photoluminescence emission at large emission angles. This degree of linear polarization of excitons can increase up to âź17% in the hBN encapsulated samples. As we confirm by finite-difference time-domain simulations, it can be directly connected to the optical anisotropy of the hBN layers. In comparison, the linear polarization at finite exciton momenta is significantly reduced in a suspendedMoSe2 monolayer, and becomes notable only in cryogenic conditions. This phenomenon strongly suggests that the effect is rooted in the k-dependent anisotropic exchange coupling inherent in2Dexcitons.Our results have strong implications on further studies on valley contrasting selection rules and valley coherence phenomena using standard suspended and encapsulated samples
The Hidradenitis Suppurativa Quality of Life (HiSQOL) score: development and validation of a measure for clinical trials
Background
Hidradenitis suppurativa (HS) is a chronic, inflammatory condition that can have a large negative impact on healthârelated quality of life (HRQOL). A reliable and validated measure of HSâspecific HRQOL in clinical studies is needed.
Objective
To develop and validate the Hidradenitis Suppurtiva Quality Of Life (HiSQOLŠ) scale, for clinical trial measurement of HSâspecific HRQOL.
Methods
Stage 1: Qualitative concept elicitation (CE) interviews were conducted with HS patients in Denmark (DK) (n = 21) and the United States (US) (n=21). Stage 2: Cognitive debriefing (CD) interviews were performed with US HS patients (n = 30) and Danish HS patients (n=30). Stage 3: Observational study of 222 HS patients in the US was conducted for item reduction, measure validation and assessment of psychometric properties. Stage 4: Observational study of 215 HS patients in Denmark was conducted to confirm the psychometric structure derived in stage 3. In both studies â the Dermatology Life Quality Index, Hospital Anxiety and Depression Scale, and numerical rating scale for pain â were also included.
Results
In CE, 99 items were generated and reduced to 41 after removing duplicates. In CD, 2 items were added and 1 items removed. A 42âitem instrument was psychometrically assessed. Based on psychometric analyses and patient input, the instrument was reduced to 17 items that had strong psychometric properties in both US and DK samples
Electron spin resonance in membrane research: proteinâlipid interactions from challenging beginnings to state of the art
Conventional electron paramagnetic resonance (EPR) spectra of lipids that are spin-labelled close to the terminal methyl end of the acyl chains are able to resolve the lipids directly contacting the protein from those in the fluid bilayer regions of the membrane. This allows determination of both the stoichiometry of lipidâprotein interaction (i.e., number of lipid sites at the protein perimeter) and the selectivity of the protein for different lipid species (i.e., association constants relative to the background lipid). Spin-label EPR data are summarised for 20 or more different transmembrane peptides and proteins, and 7 distinct species of lipids. Lineshape simulations of the two-component conventional spin-label EPR spectra allow estimation of the rate at which protein-associated lipids exchange with those in the bulk fluid regions of the membrane. For lipids that do not display a selectivity for the protein, the intrinsic off-rates for exchange are in the region of 10Â MHz: less than 10Ă slower than the rates of diffusive exchange in fluid lipid membranes. Lipids with an affinity for the protein, relative to the background lipid, have off-rates for leaving the protein that are correspondingly slower. Non-linear EPR, which depends on saturation of the spectrum at high radiation intensities, is optimally sensitive to dynamics on the timescale of spin-lattice relaxation, i.e., the microsecond regime. Both progressive saturation and saturation transfer EPR experiments provide definitive evidence that lipids at the protein interface are exchanging on this timescale. The sensitivity of non-linear EPR to low frequencies of spin exchange also allows the location of spin-labelled membrane protein residues relative to those of spin-labelled lipids, in double-labelling experiments
The words leader/lĂder and their resonances in an Italo-Latin American multinational corporation
Š 2017, Š The Author(s) 2017. The problems of âlost in translationâ are well known. Yet some terms of English managerial vocabulary, which are perfectly translatable in other languages, remain untranslated. One explanation of this phenomenon is what Linguistic anthropology call negative semantic resonances. Semantic resonances focused on the issue of which meanings can or cannot be expressed by a single word in different cultures. In this paper, based on an organisational ethnography of Latin American expatriates working for an Italo-Latin-American multinational corporation (Tubworld), we analyse the resonances of the word leader/lĂder and director, direttore, capo, guida, coordinador, caudillo among a group of expatriates; all Italian, Spanish or multilingual speakers who use English as a second language in their everyday interactions. The paper explains how the different uses contribute to create a meaning of what a leader should and should not be; someone who leads without leading, sometimes a manager. The authors, an Italian native speaker who learnt Spanish during childhood and use English as his everyday language and a Spanish native speaker, argue that Italian or Spanish speakers not only avoid the words duce and caudillo (the vernacular vocabulary for leader, not in use due to the political and cultural meaning) but also the word leader/lĂder itself, as it resonate to the other two (violent, authoritarian, autocratic, antidemocratic leadership) but furthermore because the word, a lexical loan from English, failed to encapsulate the complexity of leading multilingual organisations like Tubworld
A method for detergent-free isolation of membrane proteins in their local lipid environment.
Despite the great importance of membrane proteins, structural and functional studies of these proteins present major challenges. A significant hurdle is the extraction of the functional protein from its natural lipid membrane. Traditionally achieved with detergents, purification procedures can be costly and time consuming. A critical flaw with detergent approaches is the removal of the protein from the native lipid environment required to maintain functionally stable protein. This protocol describes the preparation of styrene maleic acid (SMA) co-polymer to extract membrane proteins from prokaryotic and eukaryotic expression systems. Successful isolation of membrane proteins into SMA lipid particles (SMALPs) allows the proteins to remain with native lipid, surrounded by SMA. We detail procedures for obtaining 25 g of SMA (4 d); explain the preparation of protein-containing SMALPs using membranes isolated from Escherichia coli (2 d) and control protein-free SMALPS using E. coli polar lipid extract (1-2 h); investigate SMALP protein purity by SDS-PAGE analysis and estimate protein concentration (4 h); and detail biophysical methods such as circular dichroism (CD) spectroscopy and sedimentation velocity analytical ultracentrifugation (svAUC) to undertake initial structural studies to characterize SMALPs (âź2 d). Together, these methods provide a practical tool kit for those wanting to use SMALPs to study membrane proteins
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