Relative Turnover Research Articles

Electrochemical Reduction of CO2 Catalyzed by Re(pyridine-oxazoline)(CO)3Cl Complexes.

A series of rhenium tricarbonyl complexes coordinated by asymmetric diimine ligands containing a pyridine moiety bound to an oxazoline ring were synthesized, structurally and electrochemically characterized, and screened for CO2 reduction ability. The reported complexes are of the type Re(N-N)(CO)3Cl, with N-N = 2-(pyridin-2-yl)-4,5-dihydrooxazole (1), 5-methyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (2), and 5-phenyl-2-(pyridin-2-yl)-4,5-dihydrooxazole (3). The electrocatalytic reduction of CO2 by these complexes was observed in a variety of solvents and proceeds more quickly in acetonitrile than in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). The analysis of the catalytic cycle for electrochemical CO2 reduction by 1 in acetonitrile using density functional theory (DFT) supports the C-O bond cleavage step being the rate-determining step (RDS) (ΔG⧧ = 27.2 kcal mol-1). The dependency of the turnover frequencies (TOFs) on the donor number (DN) of the solvent also supports that C-O bond cleavage is the rate-determining step. Moreover, the calculations using explicit solvent molecules indicate that the solvent dependence likely arises from a protonation-first mechanism. Unlike other complexes derived from fac-Re(bpy)(CO)3Cl (I; bpy = 2,2'-bipyridine), in which one of the pyridyl moieties in the bpy ligand is replaced by another imine, no catalytic enhancement occurs during the first reduction potential. Remarkably, catalysts 1 and 2 display relative turnover frequencies, (icat/ip)2, up to 7 times larger than that of I.

Factors Influencing Equity Return Correlations between China’s Pairs of A- and B-Share Markets: Effect of QFII’s Implementation

This paper was intended to examine factors influencing the correlations between A- and B-shares of individual firms, and explore the effects of Qualified Foreign Institutional Investor’s (QFII) implementation on correlations. The empirical results show that interest rate differential, relative turnover rate, relative return volatility, and market sentiment had impacts on correlation both before and after the QFII’s implementation. After its implementation, correlations became more sensitive to premium, relative turnover rate and market sentiment. Furthermore, the estimated constant term for overall market correlation became more negative (raw values from -0.3413 to -0.8815), indicating an increasing correlation between A- and B-shares’ returns. The policy implications are that much benefit of diversification into emerging markets such as paired A-and B-shares can be accomplished, together with taking several influential factors into account.

One Lump or Two? A Plurality of Pathways in Gold(III)-Catalyzed Cyclization Transforming Propargyl Acetates to a Carene-like Bicyclo[4.1.0]heptane

The bicyclo[4.1.0]heptane substructure, featured in a number of natural products, is economically formed via gold(III)-mediated cycloisomerization of a 5-acetoxy-1,6-enyne. This Ohloff–Rautenstrauch rearrangement takes place with high regio- and stereocontrol and purportedly proceeds through either of two pathways that differ in the order of major events: cyclization followed by ester migration (“cyclization first”) or its transpose (“migration first”). Implicit solvent-phase (dichloroethane) electronic structure calculations [IEFPCM-B2PLYP-D3/def2-TZVP//IEFPCM-B2PLYP/6-31G(d)-LANL2DZ] aimed at elucidation of the minimum energy pathway corresponding to the “cyclization first” and “migration first” pathways are presented herein. Both pathways feature multiple steps and are characterized by low-energy barriers, indicating that facile interconversion of structures on the surface is possible. In addition, the highest-energy structures for each of the two pathways are very close in energy (ΔΔE⧧ < 3.0 kcal/mol). Relative turnover frequency (TOF) and degree of TOF control (XTOF) calculations indicate that although a cyclization first pathway may dominate, both cyclization and acyl migration processes influence the rate of this reaction.

Turnover Dynamics of Breeding Land Birds on Islands: is Island Biogeographic Theory ‘True but Trivial’ over Decadal Time-Scales?

The theory of island biogeography has revolutionised the study of island biology stimulating considerable debate and leading to the development of new advances in related areas. One criticism of the theory is that it is ‘true but trivial’, i.e., on the basis of analyses of annual turnovers of organisms on islands, it has been posited that stochastic turnover mainly comprises rare species, or repeated immigrations and extinctions thereof, and thereby contribute little to the overall ecological dynamics. Here, both the absolute and relative turnover of breeding land birds are analysed for populations on Skokholm, Wales, over census intervals of 1, 3, 6, 12, and 24 years. As expected, over short census intervals (≤6 years), much of the turnover comprised repeated colonisations and extinctions of rare species. However, at longer intervals (12 and 24 years), a sizeable minority of species (11% of the total recorded) showed evidence of colonisation and/or extinction events despite sizeable populations (some upwards of 50 pairs). These results suggest that a longer-term view is required to take into account turnover involving more common species.

Grass Mortality and Turnover Following Core Rangeland Restoration Practices

In rangelands, management interventions have sought to minimize disturbances that decrease survival of perennial grasses to avoid compositional shifts toward less desirable species. However, the effects of rangeland management techniques on perennial grass survival and turnover are not known for individual species because the discipline has largely focused on structural metrics, measuring cover or biomass rather than tracking individual plants. In this study, we quantified perennial grass survival and recruitment in response to core rangeland restoration practices across multiple soil types to determine the potential for different interventions to cause shifts to undesirable grass community assemblages. We mapped individual grass tufts and recorded basal area annually. We used these maps to track survival and recruitment of grasses in response to mechanical brush removal, chemical woody plant control, and low-intensity prescribed burning. Additionally, we performed ordinations of the grass community to explore compositional shifts resulting from management interventions. We found perennial grass mortality to be higher for mechanically treated plots on all soil types than it was in chemically treated plots, burned plots, or untreated controls. Levels of mortality from fire were similar to baseline mortality in control plots for all soil types. However, relative species turnover was variable among soils and treatments. Brush removal only resulted in compositional shifts on sandy soils, where annual grasses and species capable of rapid expansion following disturbance became dominant. Differential responses are related to differences in species turnover, which is a function of individual grass species mortality and recruitment mediated by interactions between management approach and abiotic conditions. Given this response variability, understanding effects of management actions on perennial grass turnover and the potential for those actions to result in a community shift toward less desirable species is necessary for managers to achieve restoration goals on encroached rangelands.

Microgravity induces proteomics changes involved in endoplasmic reticulum stress and mitochondrial protection.

On Earth, biological systems have evolved in response to environmental stressors, interactions dictated by physical forces that include gravity. The absence of gravity is an extreme stressor and the impact of its absence on biological systems is ill-defined. Astronauts who have spent extended time under conditions of minimal gravity (microgravity) experience an array of biological alterations, including perturbations in cardiovascular function. We hypothesized that physiological perturbations in cardiac function in microgravity may be a consequence of alterations in molecular and organellar dynamics within the cellular milieu of cardiomyocytes. We used a combination of mass spectrometry-based approaches to compare the relative abundance and turnover rates of 848 and 196 proteins, respectively, in rat neonatal cardiomyocytes exposed to simulated microgravity or normal gravity. Gene functional enrichment analysis of these data suggested that the protein content and function of the mitochondria, ribosomes, and endoplasmic reticulum were differentially modulated in microgravity. We confirmed experimentally that in microgravity protein synthesis was decreased while apoptosis, cell viability, and protein degradation were largely unaffected. These data support our conclusion that in microgravity cardiomyocytes attempt to maintain mitochondrial homeostasis at the expense of protein synthesis. The overall response to this stress may culminate in cardiac muscle atrophy.

Drought and Recovery: Independently Regulated Processes Highlighting the Importance of Protein Turnover Dynamics and Translational Regulation in Medicago truncatula

Climate change in conjunction with population growth necessitates a systems biology approach to characterize plant drought acclimation as well as a more thorough understanding of the molecular mechanisms of stress recovery. Plants are exposed to a continuously changing environment. Extremes such as several weeks of drought are followed by rain. This requires a molecular plasticity of the plant enabling drought acclimation and the necessity of deacclimation processes for recovery and continuous growth.During drought stress and subsequent recovery, the metabolome and proteome are regulated through a sequence of molecular processes including synthesis and degradation and molecular interaction networks are part of this regulatory process. In order to study this complex regulatory network, a comprehensive analysis is presented for the first time, investigating protein turnover and regulatory classes of proteins and metabolites during a stress recovery scenario in the model legume Medicago truncatula. The data give novel insights into the molecular capacity and differential processes required for acclimation and deacclimation of severe drought stressed plants.Functional cluster and network analyses unraveled independent regulatory mechanisms for stress and recovery with different dynamic phases that during the course of recovery define the plants deacclimation from stress. The combination of relative abundance levels and turnover analysis revealed an early transition phase that seems key for recovery initiation through water resupply and is independent from renutrition. Thus, a first indication for a metabolite and protein-based load capacity was observed necessary for the recovery from drought, an important but thus far ignored possible feature toward tolerance. The data indicate that apart from the plants molecular stress response mechanisms, plasticity may be related to the nutritional status of the plant prior to stress initiation. A new perspective and possible new targets as well as metabolic mechanisms for future plant-bioengineering toward enhanced drought stress tolerance are presented.

Functional characterization of a novel β-fructofuranosidase from Bifidobacterium longum subsp. infantis ATCC 15697 on structurally diverse fructans.

In this study, we describe the isolation of a gene encoding a novel β-fructofuranosidase from Bifidobacterium longum subsp. infantis ATCC 15697, and the characterization of the enzyme, the second one found in this strain, significantly different in primary sequence to the already reported bifidobacterial β-fructofuranosidases. The gene, found through genome-mining was expressed in Escherichia coli C41(DE3). The recombinant enzyme (B.longum_l1) has a molecular weight of 75kDa, with optimal activity at 50°C, pH 6·0-6·5, and a remarkable stability with a half-life of 75·5h at 50°C. B.longum_l1 has a wide specificity for fructans, hydrolysing all substrates through an exo-type mechanism, including Oligofructose P95 (β2-1 fructooligosaccharides (FOS), DP 2-8), Raftilose Synergy 1(β2-1 FOS & inulin, DP 2-60), Raftiline HP (inulin, DP 2-60), bacterial inulin (3000kDa) and levan (8·3 & 3500kDa), Agave fructans (mixed fructans, DP 3-29) and levan-type FOS (β2-6 FOS, DP 2-8), with the highest relative activity and turnover number found for levan-type FOS. The apparent affinity of the enzyme for levan-type FOS and Oligofructose P95 was found to be 9·2 and 4·6mmoll(-1) (Km ) with a specific activity of 908 and 725μmolmin(-1) mg(-1) of protein (k2 ), respectively, more than twice the activity for sucrose. B.longum_l1 is a wide substrate specificity enzyme, which may contribute to the competitiveness and persistence of this strain in the colon. The bifidobacterial β-fructofuranosidase activity was evaluated with a wide variety of substrates including noncommercial fructans, such as levan-type and mixed agave fructans. Its activity on these substrates certainly strengthens their commercial prebiotic character and contributes to the understanding of bifidobacteria stimulation by structurally diverse fructans.

Governance and firm value: The effect of a recession

This paper examines the relationship between the firm's governance structure and its value during different economic conditions. We show that both relative industry turnover and CEO entrenchment increase during economic downturns. We also find that relative industry turnover and managerial entrenchment have opposite impacts on the value of the firm throughout the recessionary period. While industry turnover leads to an appreciation in firm value, managerial entrenchment reduces shareholders’ wealth. The negative impact of managerial entrenchment on firm value, however, outweighs the positive impact of industry turnover. Accordingly, we propose that a recession provides managers with a good opportunity to camouflage their behavior and extract more private benefits and, thus, blame the poor performance on bad economic conditions.

Food waste reduction in supermarkets – Net costs and benefits of reduced storage temperature

Food waste is a major problem and therefore measures are needed to reduce it. Since expired best-before date is a frequently cited cause of food waste in supermarkets, prolonging shelf life could reduce food waste. Longer shelf life could be achieved in different ways, e.g. reduced storage temperature. However, there is limited knowledge regarding the extent to which longer shelf life actually leads to reduced food waste, and whether the benefits of reduced waste exceed the increased energy costs of maintaining reduced storage temperature. Therefore this study calculated the net effect of reducing food waste in supermarkets by reducing the storage temperature through simulating the relationships between food waste reduction, longer shelf life, reduced storage temperature and increased energy costs.A case study was performed using three years of data on cheese, dairy, deli and meat product waste in six Swedish supermarkets, together with published data on microbiological growth at different temperatures and on the energy requirement for cold storage at different temperatures. Food waste was found to be reduced with lower storage temperature for all food products tested. This measure gave increasing net savings in terms of money and greenhouse gas emissions for meat products with decreasing storage temperature. Deli products had net savings close to zero, while for dairy and cheese products there were net losses, since the costs of reducing storage temperature exceeded the potential savings. Therefore, reducing storage temperature has the potential to reduce waste, but at a total net cost. However, a net benefit can be achieved if the measure is only introduced for products with high relative waste, low turnover and high value per unit mass.

Structure Sensitivity of the Oxygen Evolution Reaction Catalyzed by Cobalt(II,III) Oxide.

Quantum chemical calculations and simulated kinetics were used to examine the structure sensitivity of the oxygen evolution reaction on several surface terminations of Co3O4. Active sites consisting of two adjacent Co(IV) cations connected by bridging oxos were identified on both the (001) and (311) surfaces. Formation of the O-O bond proceeds on these sites by nucleophilic attack of water on a bridging oxo. It was found that the relative turnover frequencies for the different sites are highly dependent on the overpotential, with the dual-Co site on the (311) surface being most active at medium overpotentials (0.46-0.77 V), where O-O bond formation by water addition is rate limiting. A similar dual-Co site on the (001) surface is most active at low overpotentials (<0.46 V), where O2 release is rate limiting, and a single-Co site on the (110) surface is most active at overpotentials that are high enough (>0.77 V) to form a significant concentration of highly reactive terminal Co(V)═O species. Two overpotential-dependent Sabatier relationships were identified based on the Brønsted basicity and redox potential of the active site, explaining the change in the active site with overpotential. The (311) dual-Co site that is most active in the medium overpotential range is consistent with recent experimental observations suggesting that a defect site is responsible for the observed oxygen evolution activity and that a modest concentration of superoxo intermediates is present on the surface. Importantly, we find that it is essential to consider the kinetics of the water addition and O2 release steps rather than only the thermodynamics.

Is It Possible to OD on Alpha?

It is wellknown that combining multiple hedge fund alpha streams yields diversification benefits to the resultant portfolio. Additionally, crossing trades between different alpha streams reduces transaction costs: As the number of alpha streams increases, the relative turnover of the portfolio decreases with the crossing of more trades. However, Kakushadze and Liewargue that under reasonable assumptions, as the number of alphas increases, turnover does not decrease indefinitely; instead, the turnover approaches a nonvanishing limit related to the correlation structure of the portfolio’s alphas. The authors also point out that, more generally, computational simplifications can be employed when the number of alphas is large.

Resource economics and coordination among above- and below-ground functional traits of three dominant shrubs from the Chilean coastal desert

Aims Plant functional traits determine how plants respond to environmental factors and influence ecosystem processes. Among them, root traits and analyses of relations between above and below-ground traits in natural communities are scarce. We characterized a set of above- and below-ground traits of three dominant shrub species in a semiarid shrub-steppe that had contrasting leaf phenological habits (deciduous, semideciduous and evergreen). We analysed if there was coordination among above- and below-ground resource economics patterns: i.e. patterns of biomass allocation, construction costs and lifespan. Important Findings Above- and below-ground traits and their resource economics relations pointed to species-specific functional strategies to cope with drought and poor soils and to a species ranking of fast to slow whole-plant strategies in terms of resource uptake, biomass construction costs and turnover. The deciduous shrub, Proustia cuneifolia, had relatively deep and even distribution of roots, and high proportion of short-lived tissues of low C construction costs: it had high fine to coarse root and high leaf-to-stem biomass ratios, high specific leaf area (SLA), and stems of low wood density. This strategy allows Proustia to maximize and coordinate above- and belowground resources uptake as long as the most limiting factor (water) is available, but at the cost of having relative high plant biomass turnover. The evergreen Porlieria chilensis, instead, displayed a more conservative and slow strategy in terms of resource economics. It had ~80% of the roots in the 40 cm topsoil profile, low proportion of fine compared with coarse roots and low leaf-to-stem ratios, low SLA and stems of high wood density, i.e. it invested in C costly tissues that, overall, persist longer but probably at the cost of having lower plant resource uptake rates. Traits in the semideciduous Adesmia bedwellii were in between these two functional extremes. Our results revealed high functional diversity and aboveand below-ground complementarity in resource economics among these three codominant species in the Chilean coastal desert.

How Does Relative Deprivation Influence Employee Intention to Leave a Merged Company? The Role of Organizational Identification

Recognizing the importance of postmerger integration from a human resource management perspective, this study explores the relationship between employee perceptions of relative deprivation during a merger and acquisition (M&amp;A) process and their turnover intentions. Drawing on social identity theory, we investigate whether the relationship between relative deprivation and turnover intention can be mediated by employee organizational identification. The results, based on a two‐phase survey of 222 employees in a merged Korean company, show that egoistic relative deprivation, defined as people's feelings of deprivation due to their dissatisfaction with their position as an individual, predicts employee turnover intention. Moreover, employee identification with the postmerger organization was found to fully mediate the relationship between egoistic relative deprivation and turnover intention. The article concludes with theoretical contributions, practical implications, and future research directions. © 2014 Wiley Periodicals, Inc.

Is it Possible to OD on Alpha?

It is well known that combining multiple hedge fund alpha streams yields diversification benefits to the resultant portfolio. Additionally, crossing trades between different alpha streams reduces transaction costs. As the number of alpha streams increases, the relative turnover of the portfolio decreases as more trades are crossed. However, we argue, under reasonable assumptions, that as the number of alphas increases, the turnover does not decrease indefinitely; instead, the turnover approaches a non-vanishing limit related to the correlation structure of the portfolio’s alphas. We also point out that, more generally, computational simplifications can arise when the number of alphas is large.

P331 HUMAN HEPATIC HepaRG CELLS MAINTAIN HIGH INTRINSIC CYP450 ACTIVITY/METABOLISM AND SIGNIFICANTLY OUTPERFORM STANDARD HepG2/C3A CELLS USED IN DRUG PHARMACOLOGY APPLICATIONS

Introduction: Conventional in vitro human hepatic models for drug testing are based on the use of cell lines or primary human hepatocytes (PHHs). However, limited availability, inter-donor functional variability and early phenotypic alterations of PHHs in vitro restrict their use; whilst cell lines such as HepG2/C3As lack a substantial and variable set of liver-specific functions, specifically, CYP450 activity. In this study we compared CYP450 activity/ metabolism between HepG2/C3A and human HepaRG cells as hepatic models for pre-clinical drug testing. Methods: Human hepatic cell lines [HepG2/C3A or HepaRG] were grown to >80% confluence on collagen-I-coated plates and treated (in triplicates) 24 h with prototypical inducers rifampicin (CYP3A4) and omeprazole (CYP1A2), [n=3]. 50μM testosterone or phenacetin were added and supernatant and cell samples taken after 2 hours of incubation at 37°C. CYP1A2/3A4 activity [P450-Glo™-Luminometry; Promega] was determined (Figure 1). Relative turnover of testosterone [HPLC] and phenacetin [LC-MS/MS] metabolites was also measured. Cell phenotype was assessed by light-microscopy, histology (PAS-Glycogen), CYP3A4, F-actin/phalloidin, and JC-1 fluorescent-staining. Results: Figure 1 shows HepaRG CYP1A2/3A4 activity was 40-80x fold >> HepG2/C3A cells [P<0.001]; Drug profiling revealed HepaRGs had both enhanced production of major metabolites of phenacetin and testosterone and more intact drug metabolism compared with HepG2/C3A. In contrast with HepG2/C3A, HepaRGs displayed a more intact hepatic phenotype, including: Strong positive glycogen, CYP3A4 staining, high JC-1-positive intrinsic metabolic activity (ΔΨm) and organotypic gross morphology. Discussion / Conclusion: HepaRG cells may represent a more physiologically-relevant pre-clinical platform for CYP450 activation/ inhibition, safety pharmacology, as well as drug-drug interaction studies.

The Intestinal Metabolome: An Intersection Between Microbiota and Host

Recent advances that allow us to collect more data on DNA sequences and metabolites have increased our understanding of connections between the intestinal microbiota and metabolites at a whole-systems level. We can also now better study the effects of specific microbes on specific metabolites. Here, we review how the microbiota determines levels of specific metabolites, how the metabolite profile develops in infants, and prospects for assessing a person's physiological state based on their microbes and/or metabolites. Although data acquisition technologies have improved, the computational challenges in integrating data from multiple levels remain formidable; developments in this area will significantly improve our ability to interpret current and future data sets.

Homeostasis of the Cellular Actin Cortex

The cell cortex is a thin network of actin, myosin motors, and associated proteins that underlies the plasma membrane in most eukaryotic cells. It enables cells to resist extracellular stresses, perform mechanical work, and change shape. The actin network undergoes constant reorganisation due to molecular turnover. Hence, cortical structural and mechanical properties depend strongly on the relative turnover rates of its constituents and the actin filament length-distribution, but quantitative data on these dynamics remains elusive. We combined single molecule speckle microscopy and photobleaching experiments with microscopic computer simulations to analyse how molecular binding dynamics of G-actin to filaments sets network turnover and consequently the mechanical properties of the cellular actin cortex in living cells. Using photobleaching experiments, we found that two filament families with very different turnover rates composed the actin cortex: one with fast turnover dynamics and polymerisation resulting from addition of monomers to free barbed-ends and one with slow turnover dynamics with polymerisation resulting from formin-mediated filament growth. We show that filaments in the second subpopulation are on average longer than those in the first and that cofilin-mediated severing of formin-capped filaments contributes to replenishing the filament subpopulation with free barbedends. Additionally, we measured the molecular association rates and the distribution of travel-distances of actin monomers and formin dimers in speckle experiments and showed that this travel-distance distribution is consistent with the actin filament length-distribution found from photobleaching experiments and molecular simulations. Together, our results provide a quantitative characterisation of essential mechanisms underlying actin cortex homeostasis.

Abstracts: XL ESAO Annual Congress, 11-14 September 2013, Glasgow, Scotland

Objectives: The generation of an in vitro 3D organotypic human hepatic model as a surrogate for primary tissue and a platform for drug testing requires various configurations and dimensions of culture to be tested in regard to their biotransformation capabilities. We tested a non-invasive assay for dynamic functional profiling of CYP3A4 activity as a potential tool for the functional assessment of culture formats.Methods & Materials: Human hepatic cell lines [C3A or HepaRG] grown on uncoated or collagen-coated 6-well plates were induced for 24 h with rifampicinand subsequently exposed to 50 μM testosterone for 2 h, before samples were taken and measured via HPLC. Results: HepaRG cells displayed a significantly higher relative turnover of testosterone metabolites (56.47±7.60%, p<0.0001) than both C3A culture formats (Collagen-coated: 1.95±0.19%, uncoated: 2.11±0.45%). Interestingly, the test also indicated more intact metabolic pathways in HepaRGs as shown by the relative abundance of various metabolites, whereas C3A samples only contained androstenedione or in the case of C3As grown on collagen-coated dishes, low additional amounts of 16α-hydroxytestosterone (11.73 vs. 88.27±7.42%). Conclusions: The dynamic testosterone profiling assay gives insight into the relative CYP3A4 specific metabolic activity of hepatic cell lines in vitro. As such,the assay is an attractive tool for the non-invasive assessment of metabolic activity of engineered tissue constructs and the influence of extracellular matrix composition on functionality in comparison to primary tissue and is currently being applied to CYP1A2-specific metabolism.

Dynamics of the meningeal CD4+ T-cell repertoire are defined by the cervical lymph nodes and facilitate cognitive task performance in mice

The traditional view of the central nervous system (CNS) as an immune-privileged organ yielded a longstanding perception of such interactions—as seen for example in multiple sclerosis (MS) 1, 2—as intrinsically destructive. This notion is changing with the identification of several homeostatic functions attributable to beneficial T-cell/CNS interaction 3, for example in hippocampal-dependent learning 4 and stress response paradigms 5, and in models of neurodegeneration and CNS injury 6. Here we provide insights into the maintenance, and dynamics of the meningeal T-cell repertoire. We show that meningeal T-cell composition is coupled to the CNS-draining deep cervical lymph nodes (dCLNs), whose surgical removal interrupted the normal flow of meningeal T-cells and resulted in cognitive impairment.