Counteraction of Urea by Trimethylamine N-Oxide Is Due to Direct Interaction

Trimethylamine N-oxide (TMAO) is a naturally occurring osmolyte that stabilizes proteins, induces folding, and counteracts the denaturing effects of urea, pressure, and ice. To establish the mechanism behind these effects, isotopic substitution neutron-scattering measurements were performed on aqueous solutions of TMAO and 1:1 TMAO-urea at a solute mole fraction of 0.05. The partial pair distribution functions were extracted using the empirical potential structure refinement method. The results were compared with previous results obtained with isosteric tert-butanol, as well as the available data from spectroscopy and molecular-dynamics simulations. In solution, the oxygen atom of TMAO is strongly hydrogen-bonded to, on average, between two and three water molecules, and the hydrogen-bond network is tighter in water than in pure water. In TMAO-urea solutions, the oxygen atom in TMAO preferentially forms hydrogen bonds with urea. This explains why the counteraction is completed at a 2:1 urea/TMAO concentration ratio, independently of urea concentration. These results strongly support models for the effect of TMAO on the stability of proteins based on a modification of the simultaneous equilibria that control hydrogen bonding between the peptide backbone and water or intramolecular sites, without any need for direct interaction between TMAO and the protein.     

Cardiolipin fingerprinting of leukocytes by MALDI-TOF/MS as a screening tool for Barth syndrome

Barth syndrome (BTHS), an X-linked disease associated with cardioskeletal myopathy, neutropenia, and organic aciduria, is characterized by abnormalities of card­iolipin (CL) species in mitochondria. Diagnosis of the disease is often compromised by lack of rapid and widely available diagnostic laboratory tests. The present study describes a new method for BTHS screening based on MALDI-TOF/MS analysis of leukocyte lipids. This generates a “CL fingerprint” and allows quick and simple assay of the relative levels of CL and monolysocardiolipin species in leukocyte total lipid profiles. To validate the method, we used vector algebra to analyze the difference in lipid composition between controls (24 healthy donors) and patients (8 boys affected by BTHS) in the high-mass phospholipid range. The method of lipid analysis described represents an important additional tool for the diagnosis of BTHS and potentially enables therapeutic monitoring of drug targets, which have been shown to ameliorate abnormal CL profiles in cells.     

Ecological re-engineering of a freshwater impoundment for salt marsh restoration in a hypertidal system

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic response to ecological re-engineering of a freshwater impoundment in the Upper Bay of Fundy. The dyke was breached in five locations and one channel initiated to connect the river to the borrow pit behind the dyke. This triggered significant self-organization within the restoration site. Existing channels (e.g. borrow pit) were incorporated within the newly excavated and developing creek system, increasing the hydraulic connectivity within the marsh and increasing fish habitat. Vegetation colonization, primarily by Spartina alterniflora, was rapid with almost 100% coverage by the end of the third year. Species associated with high marsh communities such as Juncus gerardii, Scirpus robustus, Ranunculus cymbalaria and Puccinellia maritima were present in increasing abundance post-restoration at the restoration site. The constructed channel eroded downward 2.3 m and the head of the channel retreated 35 m in response to the increased tidal prism. In the year immediately following the breach (2006), the surface of the marsh was unconsolidated and rates of change in surface elevation measured at RSET stations ranged from ?0.7 (±0.1) to 1.7 (±0.2) cm yr^?1 (±1SE). Measurements between years are highly variable. By year 3 the rate of surface elevation change decreased to a more moderate but variable mean of 0.3 (±0.6) cm yr^?1 with the marker horizons recording mean accretion rates of 0.7 cm yr^?1. This implies subsurface consolidation as the sediments dewatered or organic matter decomposed and vegetation became more established. Fish density decreased after restoration, however, remained higher than at the reference site for most years.     

Effect of enteral nutritional products differing in carbohydrate and fat on indices of carbohydrate and lipid metabolism in patients with NIDDM

Non-insulin dependent diabetes mellitus (NIDDM) is associated with chronic hyperglycemia, which increases the risk of developing microvascular and macrovascular complications. Elevated triglyceride (TG) and VLDL cholesterol levels and low levels of HDL cholesterol have also been frequently reported in NIDDM patients. A diet high in complex carbohydrate and low in fat is typically recommended for management of NIDDM, however, this has recently been challenged by scientific reports of the benefits of dietary intakes high in monounsaturated fat. Thirty-two individuals with NIDDM were randomized to receive either Ensure with Fibre® (30% fat) or a high monounsaturated fatty acid product, Glucerna® (50% fat). These products were consumed for 28 days at 280% of daily energy intake. Post-treatment, dietary compliance was verified by a higher plasma TG 18:1 n-9 (p < 0.001) in the Glucerna® group and a higher plasma TG 18:2 n-6 (p < 0.001) in the Ensure with Fibre® group. The postprandial rise in blood glucose levels, determined by fingerprick samples, was significantly lower (p < 0.01) in the Glucerna® group. Trends of clinical interest were greater mean decreases in the Glucerna® group compared to the Ensure with Fibre® group in: fructosamine, 9.13 umol/L vs 0.14 umol/L; glucose, 1.61 mmol/L vs 0.63 mmol/L; and insulin, 46.0 pmol/L vs 12.6 pmol/L; respectively. However, overall, fasting plasma glucose, fructosamine, TG and cholesterol levels were not significantly different between groups. Thus, in these patients, the high monounsaturated fat diet and the standard diet were similar with regard to usual indicators of carbohydrate and lipid metabolism. A high monounsaturated fat diet appears to pose no risk to lipoprotein metabolism in NIDDM patients.     

Molecular and mesoscale structures in hydrophobically driven aqueous solutions

Since Kauzmann's seminal 1959 paper, the hydrophobic interaction has dominated thinking on the forces that control protein folding and stability. Despite its wide importance in chemistry and biology, our understanding of this interaction at the molecular level remains poor, with little experimental evidence to support the idea of water ordering close to a non-polar group that is at the centre of the standard model for the source of the entropic driving force. Developments over recent years in neutron techniques now enable us to see directly how a non-polar group actually affects the molecular structure of the water in its immediate neighbourhood. On the basis of such work on aqueous solutions of small alcohols, the generally accepted standard model is found to be wanting, and alternative sources of the entropic driving force are suggested. Moreover, the fact that we can now follow changes in hydrogen bonding as the alcohol concentration is varied gives us the possibility of explaining the concentration dependence of the enthalpy of mixing. Complementary studies of solute association on the mesoscopic scale show a rich concentration and temperature behaviour, which reflects a complex balance of polar and non-polar interactions. Unravelling the detailed nature of this balance in simple aqueous amphiphiles may lead to a better understanding of the forces that control biomolecular structural stability and interactions.     

Structure and interactions in simple solutions

Neutron scattering with hydrogen/deuterium isotopic substitution techniques has been used to investigate the full range of structural interactions in a dilute 0.02 mol fraction solution of tertiary butanol in water, both in the absence and in the presence of a small amount of sodium chloride. Emphasis is given to the detailed pictures of the intermolecular interactions that have been derived using the empirical potential structure refinement technique. Analysis has been performed to the level of the spatial density distribution functions that illustrate the orientational dependence of the intermolecular interactions between all combinations of molecular and ionic components. The results show the key structural motifs involved in the interactions between the various components in a complex aqueous system. They underline the structural versatility of the water molecule in accommodating a range of different kinds of interactions while retaining its characteristic first-neighbour interaction geometry. Within this framework, the results highlight the complex interplay between the polar, non-polar and charged molecular interactions that exist in the system.     

Hitchhiking halophytes in wrack and sediment-laden ice blocks contribute to tidal marsh development in the Upper Bay of Fundy

Wetlands Ecology and Management - Salt marshes are a type of coastal wetland that are affected by dynamic coastal processes. Ice blocks and wrack (mats of plant debris) regularly float onto...     

Macro‐Tidal Salt Marsh Ecosystem Response to Culvert Expansion

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic conditions pre‐restoration and the initial 2 years post‐restoration at a partially restricted macro‐tidal salt marsh site. Replacement of the culvert increased tidal flow by 88%. This was instrumental in altering the geomorphology of the site, facilitating the creation of new salt marsh pannes, expansion of existing pannes in the mid and high marsh zones, and expansion of the tidal creek network by incorporating relict agricultural ditches. In addition, the increase in area flooded resulted in a significant increase in nekton use, fulfilling the mandate of a federal habitat compensation program to increase and improve the overall availability and accessibility of fish habitat. The restoration of a more natural hydrological regime also resulted in the die‐off of freshwater and terrestrial vegetation along the upland edge of the marsh. Two years post‐restoration, Salicornia europea (glasswort) and Atriplex glabriuscula (marsh orache), were observed growing in these die‐back areas. Similar changes in the vegetation community structure were not observed at the reference site; however, the latter did contain higher species richness. This study represents the first comprehensive, quantitative analysis of ecological response to culvert replacement in a hypertidal ecosystem. These data will contribute to the development of long‐term data sets of pre‐ and post‐restoration, and reference marsh conditions to determine if a marsh is proceeding as expected, and to help with models that are aimed at predicting the response of marshes to tidal restoration at the upper end of the tidal spectrum.