Home About us Contact
|
Home About us Contact | ||
|
|
||
Complex Effects (complex + effects)
Selected AbstractsSimple Transfers, Complex Outcomes: The Impacts of Pensions on Poor Households in BrazilDEVELOPMENT AND CHANGE, Issue 5 2006Peter Lloyd-Sherlock ABSTRACT Drawing on quantitative survey data and in-depth interviews, this article seeks to map out the potential direct and indirect effects of simple cash transfers on households in impoverished rural and urban settings. Brazil is shown to have an extensive system of old age pensions, which affords almost universal coverage to households containing older people. These benefits have a significant impact on levels of poverty and vulnerability in recipient households. They also facilitate access to essential healthcare items, such as drugs, which are seldom freely available through the state health system. The in-depth interviews reveal that pensions can have important effects on intra-household relations, but these effects were not generalizable nor easily captured by quantitative survey tools. There was clear evidence that pensions reduced the propensity of older people to remain economically active, but this must be understood in a context of limited employment opportunities for all age groups and a high prevalence of disability. Overall, the article demonstrates the complex effects of a relatively simple cash transfer, which policy makers need to take into account. [source] Understanding biodiversity effects on prey in multi-enemy systemsECOLOGY LETTERS, Issue 9 2006Paolo Casula Abstract Biodiversity,ecosystem functioning theory would predict that increasing natural enemy richness should enhance prey consumption rate due to functional complementarity of enemy species. However, several studies show that ecological interactions among natural enemies may result in complex effects of enemy diversity on prey consumption. Therefore, the challenge in understanding natural enemy diversity effects is to predict consumption rates of multiple enemies taking into account effects arising from patterns of prey use together with species interactions. Here, we show how complementary and redundant prey use patterns result in additive and saturating effects, respectively, and how ecological interactions such as phenotypic niche shifts, synergy and intraguild predation enlarge the range of outcomes to include null, synergistic and antagonistic effects. This study provides a simple theoretical framework that can be applied to experimental studies to infer the biological mechanisms underlying natural enemy diversity effects on prey. [source] A Brief Commentary on the Hegelian-Marxist Origins of Gramsci's ,Philosophy of Praxis'EDUCATIONAL PHILOSOPHY AND THEORY, Issue 6 2009Debbie J Hill Abstract The specific nuances of what Gramsci names ,the new dialectic' are explored in this paper. The dialectic was Marx's specific ,mode of thought' or ,method of logic' as it has been variously called, by which he analyzed the world and man's relationship to that world. As well as constituting a theory of knowledge (epistemology), what arises out of the dialectic is also an ontology or portrait of humankind that is based on the complete historicization of humanity; its ,absolute "historicism"' or ,the absolute secularisation and earthliness of thought', as Gramsci worded it (Gramsci, 1971, p. 465). Embracing a fully secular and historical view of humanity, it provides a vantage point that allows the multiple and complex effects of our own conceptual heritage to be interrogated in relation to our developing ,nature' or ,being'. The argument presented in this paper is that the legacy of both Hegel and Marx is manifest in the depth of Gramsci's comprehension of what he termed the ,educative-formative' problem of hegemony. It is precisely the legacy of this Hegelian-Marxist radical philosophical critique that is signified in his continuing commitment to the ,philosophy of praxis' and the historical-dialectical principles that underpin this worldview. [source] Quantitative trait association in parent offspring trios: Extension of case/pseudocontrol method and comparison of prospective and retrospective approachesGENETIC EPIDEMIOLOGY, Issue 8 2007Eleanor Wheeler Abstract The case/pseudocontrol method provides a convenient framework for family-based association analysis of case-parent trios, incorporating several previously proposed methods such as the transmission/disequilibrium test and log-linear modelling of parent-of-origin effects. The method allows genotype and haplotype analysis at an arbitrary number of linked and unlinked multiallelic loci, as well as modelling of more complex effects such as epistasis, parent-of-origin effects, maternal genotype and mother-child interaction effects, and gene-environment interactions. Here we extend the method for analysis of quantitative as opposed to dichotomous (e.g. disease) traits. The resulting method can be thought of as a retrospective approach, modelling genotype given trait value, in contrast to prospective approaches that model trait given genotype. Through simulations and analytical derivations, we examine the power and properties of our proposed approach, and compare it to several previously proposed single-locus methods for quantitative trait association analysis. We investigate the performance of the different methods when extended to allow analysis of haplotype, maternal genotype and parent-of-origin effects. With randomly ascertained families, with or without population stratification, the prospective approach (modeling trait value given genotype) is found to be generally most effective, although the retrospective approach has some advantages with regard to estimation and interpretability of parameter estimates when applied to selected samples. Genet. Epidemiol. 2007. © 2007 Wiley-Liss, Inc. [source] Evolutionary-based grouping of haplotypes in association analysisGENETIC EPIDEMIOLOGY, Issue 3 2005Jung-Ying Tzeng Abstract Haplotypes incorporate more information about the underlying polymorphisms than do genotypes for individual SNPs, and are considered as a more informative format of data in association analysis. To model haplotypes requires high degrees of freedom, which could decrease power and limit a model's capacity to incorporate other complex effects, such as gene-gene interactions. Even within haplotype blocks, high degrees of freedom are still a concern unless one chooses to discard rare haplotypes. To increase the efficiency and power of haplotype analysis, we adapt the evolutionary concepts of cladistic analyses and propose a grouping algorithm to cluster rare haplotypes to the corresponding ancestral haplotypes. The algorithm determines the cluster bases by preserving common haplotypes using a criterion built on the Shannon information content. Each haplotype is then assigned to its appropriate clusters probabilistically according to the cladistic relationship. Through this algorithm, we perform association analysis based on groups of haplotypes. Simulation results indicate power increases for performing tests on the haplotype clusters when compared to tests using original haplotypes or the truncated haplotype distribution. Genet. Epidemiol. © 2005 Wiley-Liss, Inc. [source] EXPLORING THE CONNECTIONS: LAND TENURE, SOCIAL IDENTITIES, AND AGROBIODIVERSITY PRACTICES IN GHANAGEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 2 2009Louis Awanyo ABSTRACT. This article employs qualitative and quantitative evidence from primary social research in Ghana to examine the link between land tenure security and social identities (of wealth/income and gender), and how they condition farmers' investments in practices that contribute to the rehabilitation of tree biodiversity (agrobiodiversity). Statistical analyses of the significance of the effects of farmers' de jure land tenure security regimes, and income and gender on agrobiodiversity practices were inconclusive. The conventional causation link between investments and more secure formal land tenure rights, for instance, was confirmed in investments in four out of eight agrobiodiversity practices. Testimonial-based evidence of farmers provided a clearer concept of land tenure security and an explanatory framework about the interacting and complex effects of income and gender on land tenure security. The theoretical and empirical argument developed from these testimonies portrays land tenure as embodying negotiated social processes, influenced by gender and income of individuals, whereby breadth of land rights, duration of rights over land, and assurance of rights are established, sustained, enhanced or changed through a variety of strategies to shape tenure security. These processes , tenure building and renewal processes , are critical because all farmers have lingering anxiety about land tenure rights, even among farmers with more secure formal rights. Investments are made in agrobiodiversity practices as a strategy to strengthen land tenure security and thereby minimize anxiety, leading to reverse causation effects between land tenure, social identities, and investments. [source] Action of Force on Rock Mass by Crack Water PressureGEOMECHANICS AND TUNNELLING, Issue 6 2008Guntram Innerhofer Dipl.-Ing. The formula of effective stress used in soil mechanics is adapted to the properties of rock mass by implementation of the wetting factor and the Saint-Venant factor. The wetting factor defines the area over which a hydrostatic force can actually be developed, the Saint Venant factor defines the component of this force which is balanced by reduction of the effective stress in the crack zone. Here, the consequences of this concept are discussed with respect to uniaxial, plain stress and a continuum mechanical model. The effect of the concept is considered in relation to the state of stress in crack zones, and in the adjacent rock mass, and on the action of forces on the system. The development of crack propagation and of shear failure is discussed. The intention is to contribute towards a basic understanding of the complex effects of water pressure in rock masses, applicable to engineering practice. Kraftwirkung des Kluftwasserdrucks auf Fels Die Formel für Effektivspannungen der Bodenmechanik wird, den Eigenschaften von Fels entsprechend, durch Einführen des Benetzungsgrads und des Saint-Venant-Faktors erweitert. Der Benetzungsgrad definiert die Fläche, auf die eine hydrostatische Kraft wirken kann, der Saint-Venant-Faktor die Komponente dieser Kraft, die in der Kluftfläche durch Reduktion der Effektivspannungen ausgeglichen wird. Die andere Komponente belastet das System. Anhand eines einachsigen, eines ebenen und eines Kontinuum-Mechanischen Modells werden die aus diesem Ansatz abgeleiteten Spannungszustände in der Kluftfläche beziehungsweise im klüftigen Fels diskutiert. Die Entwicklung von Kluftsprengung und Scherbruch und das Verhalten hoch- und tiefliegender Druckstollen werden beschrieben. Beabsichtigt ist, mit einer möglichst geschlossenen, auf das Wesentliche beschränkten Darstellung das Verständnis der komplexen Zusammenhänge zu fördern. [source] Immune regulation by 4-1BB and 4-1BBL: complexities and challengesIMMUNOLOGICAL REVIEWS, Issue 1 2009Chao Wang Summary:, The tumor necrosis factor receptor family member 4-1BB plays a key role in the survival of activated and memory CD8+ T cells. Depending on the disease model, 4-1BB can participate at different stages and influence different aspects of the immune response, likely due to the differential expression of receptor and ligand relative to other costimulatory molecules. Studies comparing mild versus severe influenza infection of mice suggest that the immune system uses inducible receptors such as 4-1BB to prolong the immune response when pathogens take longer to clear. The expression of 4-1BB on diverse cell types, evidence for bidirectional as well as receptor-independent signaling by 4-1BBL, the unexpected hyperproliferation of 4-1BB-deficient T cells, and complex effects of agonistic anti-4-1BB therapy have revealed additional roles for the 4-1BB/4-1BBL receptor/ligand pair in the immune system. In this review, we discuss these diverse roles of 4-1BB and its ligand in the immune response, exploring possible mechanisms for the observed complexities and implications for therapeutic applications of 4-1BB/4-1BBL. [source] The role of research for integrated management of invasive species, invaded landscapes and communitiesJOURNAL OF APPLIED ECOLOGY, Issue 2 2008Yvonne M. Buckley Summary 1Invaded landscapes and ecosystems are composed of multiple interacting networks and feed-back loops, sometimes leading to unexpected effects of management actions. In order to plan management for invaded systems we need to explicitly consider management goals before putting actions in place. Actions taken must be justified in terms of their amelioration of impacts of invaders, contribution to the management goals and the costs incurred. 2This Special Profile brings together papers on the management of invasive plants, transgenes, animals and diseases, leading to conclusions with clear policy and management relevance and contributing to some of the hottest current topics in invasion ecology: unexpected impacts of invaders, restoration of invasion resistance, distribution mapping, spatial epidemiology, escape of transgenes, community interactions and complex effects of management. 3As papers in this Special Profile demonstrate, management for amelioration of the impacts of invasive species will include a wide range of manipulations, not just of the invader itself but of both abiotic and biotic components of the system. In fact, several papers in this Special Profile show that indirect management of the community may be more effective than removal of the invader alone. 4As little information is generally available at the beginning of a management programme, an adaptive approach should be taken and the management objectives/goals revised throughout the management process. New methods are emerging for adaptive management; an example is presented in this Special Profile where a Bayesian model used for assessing eradication goals can be updated throughout the management process leading to refinement of management. 5Synthesis and applications. Applied research should be directed at providing decision support for managers throughout the management process and can be used to provide predictive tools for risk assessment of new invaders. The science of invasion ecology has much to contribute to the new challenge of natural or enhanced movement of organisms in relation to climate change. Methods and information from invasion ecology can be used to assess management goals, management actions and the risks of potential translocations before they are put in place. [source] Dietary restriction affects lifespan but not cognitive aging in Drosophila melanogasterAGING CELL, Issue 3 2010Joep M.S. Burger Summary Dietary restriction extends lifespan in a wide variety of animals, including Drosophila, but its relationship to functional and cognitive aging is unclear. Here, we study the effects of dietary yeast content on fly performance in an aversive learning task (association between odor and mechanical shock). Learning performance declined at old age, but 50-day-old dietary-restricted flies learned as poorly as equal-aged flies maintained on yeast-rich diet, even though the former lived on average 9 days (14%) longer. Furthermore, at the middle age of 21 days, flies on low-yeast diets showed poorer short-term (5 min) memory than flies on rich diet. In contrast, dietary restriction enhanced 60-min memory of young (5 days old) flies. Thus, while dietary restriction had complex effects on learning performance in young to middle-aged flies, it did not attenuate aging-related decline of aversive learning performance. These results are consistent with the hypothesis that, in Drosophila, dietary restriction reduces mortality and thus leads to lifespan extension, but does not affect the rate with which somatic damage relevant for cognitive performance accumulates with age. [source] Differing effects of substrate and non-substrate transport inhibitors on glutamate uptake reversalJOURNAL OF NEUROCHEMISTRY, Issue 6 2001Christopher M. Anderson Na+ -dependent excitatory amino acid transporters (EAATs) normally function to remove extracellular glutamate from brain extracellular space, but EAATs can also increase extracellular glutamate by reversal of uptake. Effects of inhibitors on EAATs can be complex, depending on cell type, whether conditions favor glutamate uptake or uptake reversal and whether the inhibitor itself is a substrate for the transporters. The present study assessed EAAT inhibitors for their ability to inhibit glutamate uptake, act as transporter substrates and block uptake reversal in astrocyte and neuron cultures. lthreo -,-hydroxyaspartate (l -TBHA), dlthreo -,-benzyloxyaspartate (dl -TBOA), ltrans -pyrrolidine-2,4-dicarboxylic acid (ltrans -2,4-PDC) (+/,)- cis -4-methy- trans -pyrrolidine-2,4-dicarboxylic acid (cis -4-methy- trans -2,4-PDC) and lantiendo -3,4-methanopyrrolidine-2,4-dicarboxylic acid (lantiendo -3,4-MPDC) inhibited l -[14C]glutamate uptake in astrocytes with equilibrium binding constants ranging from 17 µm (dl -TBOA and l -TBHA) , 43 µm (cis -4-methy- trans -2,4-PDC). Transportability of inhibitors was assessed in astrocytes and neurons. While l -TBHA, ltrans -2,4-PDC, cis -4-methy- trans -2,4-PDC and lantiendo -3,4-MPDC displayed significant transporter substrate activities in neurons and astrocytes, dl -TBOA was a substrate only in astrocytes. This effect of dl -TBOA was concentration-dependent, leading to complex effects on glutamate uptake reversal. At concentrations low enough to produce minimal dl -TBOA uptake velocity (, 10 µm), dl -TBOA blocked uptake reversal in ATP-depleted astrocytes; this blockade was negated at concentrations that drove substantial dl -TBOA uptake (> 10 µm). These findings indicate that the net effects of EAAT inhibitors can vary with cell type and exposure conditions. [source] MicroRNAs: Master Regulators of Ethanol Abuse and Toxicity?ALCOHOLISM, Issue 4 2010Rajesh C. Miranda Ethanol exerts complex effects on human physiology and health. Ethanol is not only addictive, but it is also a fetal teratogen, an adult neurotoxin, and an etiologic agent in hepatic and cardiovascular disease, inflammation, bone loss, and fracture susceptibility. A large number of genes and signaling mechanisms have been implicated in ethanol's deleterious effects leading to the suggestion that ethanol is a "dirty drug." An important question is, are there cellular "master-switches" that can explain these pleiotropic effects of ethanol? MicroRNAs (miRNAs) have been recently identified as master regulators of the cellular transcriptome and proteome. miRNAs play an increasingly appreciated and crucial role in shaping the differentiation and function of tissues and organs in both health and disease. This critical review discusses new evidence showing that ethanol-sensitive miRNAs are indeed regulatory master-switches. More specifically, miRNAs control the development of tolerance, a crucial component of ethanol addiction. Other drugs of abuse also target some ethanol-sensitive miRNAs suggesting that common biochemical mechanisms underlie addiction. This review also discusses evidence that miRNAs mediate several ethanol pathologies, including disruption of neural stem cell proliferation and differentiation in the exposed fetus, gut leakiness that contributes to endotoxemia and alcoholic liver disease, and possibly also hepatocellular carcinomas and other gastrointestinal cancers. Finally, this review provides a perspective on emerging investigations into potential roles of miRNAs as mediators of ethanol's effects on inflammation and fracture healing, as well as the potential for miRNAs as diagnostic biomarkers and as targets for therapeutic interventions for alcohol-related disorders. [source] Preservation potential for Late Quaternary river alluviumJOURNAL OF QUATERNARY SCIENCE, Issue 2 2003John Lewin Abstract Valley sequences of Late Quaternary alluvial units reflect alluvial preservation as well as alluvial production factors. Effects of lateral channel migration, incision, aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets: cartographically dated and model data based on lateral channel migration; well-mapped and dated Late Quaternary valley unit surveys; and composite age,frequency plots for dated alluvial units and flood sediments. Despite much expectable variation between sites, and the complex effects of river-activity combinations, a common characteristic of the data sets examined is the significance of preservation factors. Lateral migration tends to eliminate older units as it creates new alluvial deposits, whereas incision may lead to the preferential preservation of older units beyond the incision slot. Aggradational environments are likely to preserve more complete records, although simultaneous lateral migration may eliminate, possibly repeatedly, the upper parts of alluvial units. The common pattern of inset and incised streams within Pleistocene and early Holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley-floor units is necessarily at the expense of reprocessing earlier ones. Floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials, thus limiting the preserved record of earlier events. In light of these censoring effects of river activities, the sequence of preserved Late Quaternary units within UK sequences is reconsidered. It is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record, and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive. Copyright © 2003 John Wiley & Sons, Ltd. [source] Exploitation of the complex chemistry of hindered amine stabilizers in effective plastics stabilization,JOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2007J. Pospí Hindered amine stabilizers (HAS) remain a prominent class of stabilizers having a fortunate development with continuous interest in shaping the future properties of plastics: increase in polymer durability, application extension, reaching new effects. Commercial tests provided much information. Insufficient mechanistic interpretations of the complex effects of environmental factors (harshness of testing, penetration of radiation and oxygen, superposition of temperature, atmospheric impurities) and those of the microenvironment (morphology of the polymer matrix, physical relations of HAS,polymer, interference between HAS and other additives) are a drawback. Model experiments complement commercial studies and explain some phenomena. A careful transfer of information from model experiments must be done to avoid misinterpretation of mechanisms, particularly of the HAS regenerative cycle. A critical analysis of primary steps of the HAS activity mechanism in the polymer matrix based on HAS-related primary nitroxides, formation of their stationary concentration and concentration gradients influenced by polymer morphology, spatial competition between autoreactions, and oxidation of polymer-developed alkyl radicals and their scavenging by nitroxides (the key process of HAS efficiency) is outlined. Cyclic regeneration of nitroxides affected by the structure of the amino moiety in the HAS molecule, influence of acid environment, atmospheric ozone or singlet oxygen, cooperative mixtures of HAS with UV absorbers, combinations with additives increasing the thermal stabilization effect and improving color retention, assessment of the heat stabilization performance of HAS by proper testing, and influence of the molecular weight of HAS are mentioned together with examples of the chemical consumption of HAS in the final phases of their lifetime. lifetime. J. VINYL ADDIT. TECHNOL., 13:119,132, 2007. © 2007 Society of Plastics Engineers [source] Assessment of lovastatin application as tool in probing cytokinin-mediated cell cycle regulationPHYSIOLOGIA PLANTARUM, Issue 2 2005Katja Hartig Lovastatin, a potent inhibitor of the mevalonate pathway, has been used in plant cell cycle studies to eliminate the cytosolic cytokinin biosynthesis. However, several implications can blur the results, as cytokinins may be alternatively formed from isopentenylpyrophosphate produced by the plastid 1-deoxy-xylulose 5-phosphate pathway and because the endogenous cytokinin levels oscillate considerably in the course of a cell cycle. In the work presented here, short- and long-term effects of lovastatin on suspension- cultured Nicotiana tabacum (L.) BY-2 cells were differentiated. The short-term experiments revealed a fast action of lovastatin, resulting in a significantly, though not completely, decreased content of endogenous cytokinins that became visible already after 10 min and was most pronounced after 30 min. But the impact of lovastatin on cell cycle progression depended also on the phase of the cell cycle at which it was administered. Lowering of the cytokinin level during the early S phase, when the endogenous cytokinin levels increased, delayed the S/G2 transition, whereas the same treatment in the late S phase, when the cellular cytokinin concentrations had already started to decrease, promoted it. Incubation periods longer than 48 h resulted in about 50% loss of viable of the cells and also in a reduced capability of division of the survivors. These cells later on resumed cell division. A second treatment with lovastatin of that culture again killed about 50% of the cells, but the surviving cells showed faster re-growth. In conclusion, lovastatin appears as a useful inhibitor of cytokinin biosynthesis in short-term studies, but its use in long-term experiments may create complex effects and therefore requires substantial caution. [source] Lessons on orographic precipitation from the Mesoscale Alpine ProgrammeTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 625 2007Richard Rotunno Abstract Although moisture-laden airflow towards a mountain is a necessary ingredient, the results from the Mesoscale Alpine Programme (MAP) demonstrate that detailed knowledge of the orographically modified flow is crucial for predicting the intensity, location and duration of orographic precipitation. Understanding the orographically modified flow as it occurs in the Alps is difficult since it depends on the static stability of the flow at low levels, which is heavily influenced by synoptic conditions, the complex effects of latent heating, and the mountain shape, which has important and complicated variations on scales ranging from a few to hundreds of kilometres. Central themes in all of the precipitation-related MAP studies are the ways in which the complex Alpine orography influences the moist, stratified airflow to produce the observed precipitation patterns, by determining the location and rate of upward air motion and triggering fine-scale motions and microphysical processes that locally enhance the growth and fallout of precipitation. In this paper we review the major findings from the MAP observations and describe some new research directions that have been stimulated by MAP results. Copyright © 2007 Royal Meteorological Society [source] Complex immunomodulatory effects of interferon-, in multiple sclerosis include the upregulation of T helper 1-associated marker genesANNALS OF NEUROLOGY, Issue 3 2001Klaus-Peter Wandinger MD Multiple sclerosis (MS) is considered an autoimmune disease that is mediated by proinflammatory T helper-1 lymphocytes. The putative mechanism of interferon-, (IFN-,), an approved treatment for MS, includes the inhibition of T-cell proliferation, blocking of blood-brain-barrier opening and T-cell transmigration into the brain via interference with cell adhesion, and the upregulation of anti-inflammatory (TH2) cytokines. In the present study, a gene expression analysis of IFN-,-treated peripheral blood mononuclear cells by cDNA microarray documents the broad effects of IFN-, that are not purely anti-inflammatory. Specifically, we addressed the effect of IFN-, on T helper-1 differentiation- or lineage markers such as the IL-12 receptor ,2 chain and the chemokine receptor CCR5 that have been implicated in the pathogenesis of MS. Both markers were significantly upregulated in vitro and in vivo under IFN-, therapy, supporting that this cytokine exerts complex effects on the immune system. The combination of cDNA microarray and quantitative polymerase chain reaction will expand our knowledge of the immunological effects of such pleiotropic agents as IFN-,, may provide a key to why certain patients fail to respond, and eventually influence our view of the disease pathogenesis. [source] ESTIMATING THE RELATIONSHIP BETWEEN IMMIGRANT AND NATIVE WORKERS IN AUSTRALIA: A PRODUCTION THEORY APPROACHAUSTRALIAN ECONOMIC PAPERS, Issue 1 2010JAAI PARASNIS The impact of immigration on labour markets depends, among other factors, on the substitutability or complementarity between immigrants and natives. This relationship is examined by treating migrant and native labour, along with capital, as inputs in production process. Estimated price elasticities of substitution between immigrants and native labour suggest that in Australian context, an increase in the wage rate of one group of workers leads to an increased demand for the other. The estimated elasticities of substitution between immigrant and native workers and the complementary relationship between immigrants and capital provide an insight into the complex effects of immigration. [source] Use of thallium to identify monovalent cation binding sites in GroELACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2009Philip D. Kiser GroEL is a bacterial chaperone protein that assembles into a homotetradecameric complex exhibiting D7 symmetry and utilizes the co-chaperone protein GroES and ATP hydrolysis to assist in the proper folding of a variety of cytosolic proteins. GroEL utilizes two metal cofactors, Mg2+ and K+, to bind and hydrolyze ATP. A K+ -binding site has been proposed to be located next to the nucleotide-binding site, but the available structural data do not firmly support this conclusion. Moreover, more than one functionally significant K+ -binding site may exist within GroEL. Because K+ has important and complex effects on GroEL activity and is involved in both positive (intra-ring) and negative (inter-ring) cooperativity for ATP hydrolysis, it is important to determine the exact location of these cation-binding site(s) within GroEL. In this study, the K+ mimetic Tl+ was incorporated into GroEL crystals, a moderately redundant 3.94,Å resolution X-ray diffraction data set was collected from a single crystal and the strong anomalous scattering signal from the thallium ion was used to identify monovalent cation-binding sites. The results confirmed the previously proposed placement of K+ next to the nucleotide-binding site and also identified additional binding sites that may be important for GroEL function and cooperativity. These findings also demonstrate the general usefulness of Tl+ for the identification of monovalent cation-binding sites in protein crystal structures, even when the quality and resolution of the diffraction data are relatively low. [source] Amino acid and manganese supplementation modulates the glycosylation state of erythropoietin in a CHO culture systemBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2007Christopher K. Crowell Abstract The manufacture of secreted proteins is complicated by the need for both high levels of expression and appropriate processing of the nascent polypeptide. For glycoproteins, such as erythropoietin (EPO), posttranslational processing involves the addition of oligosaccharide chains. We initially noted that a subset of the amino acids present in the cell culture media had become depleted by cellular metabolism during the last harvest cycle in our batch fed system and hypothesized that by supplementing these nutrients we would improve EPO yields. By increasing the concentration of these amino acids we increased recombinant human erythropoietin (rHuEPO) biosynthesis in the last harvest cycle as expected but, surprisingly, we also observed a large increase in the amount of rHuEPO with a relatively low sialic acid content. To understand the nature of this process we isolated and characterized the lower sialylated rHuEPO pool. Decreased sialylation correlated with an increase in N-linked carbohydrates missing terminal galactose moieties, suggesting that ,-1,4-galactosyltransferase may be rate limiting in our system. To test this hypothesis we supplemented our cultures with varying concentrations of manganese (Mn2+), a cofactor for ,-1,4-galactosyltransferase. Consistent with our hypothesis we found that Mn2+ addition improved galactosylation and greatly reduced the amount of rHuEPO in the lower sialylated fraction. Additionally, we found that Mn2+ addition increased carbohydrate site occupancy and narrowed carbohydrate branching to bi-antennary structures in these lower sialylated pools. Surprisingly Mn2+ only had this effect late in the culture process. These data indicate that the addition of Mn2+ has complex effects on stressed batch fed cultures. Biotechnol. Bioeng. 2007;96: 538,549. © 2006 Wiley Periodicals, Inc. [source] Role of nutrient supply on cell growth in bioreactor design for tissue engineering of hematopoietic cellsBIOTECHNOLOGY & BIOENGINEERING, Issue 7 2005Pragyansri Pathi Abstract In the present study, a dynamic mathematical model for the growth of granulocyte progenitor cells in the hematopoietic process is developed based on the principles of diffusion and chemical reaction. This model simulates granulocyte progenitor cell growth and oxygen consumption in a three-dimensional (3-D) perfusion bioreactor. Material balances on cells are coupled to the nutrient balances in 3-D matrices to determine the effects of transport limitations on cell growth. The method of volume averaging is used to formulate the material balances for the cells and the nutrients in the porous matrix containing the cells. All model parameters are obtained from the literature. The maximum cell volume fraction reached when oxygen is depleted in the cell layer at 15 days and is nearly 0.63, corresponding to a cell density of 2.25 × 108 cells/mL. The substrate inhibition kinetics for cell growth lead to complex effects with respect to the roles of oxygen concentration and supply by convection and diffusion on cell growth. Variation in the height of the liquid layer above the cell matrix where nutrient supply is introduced affected the relative and absolute amounts of oxygen supply by hydrodynamic flow and by diffusion across a gas permeable FEP membrane. Mass transfer restrictions of the FEP membrane are considerable, and the supply of oxygen by convection is essential to achieve higher levels of cell growth. A maximum growth rate occurs at a specific flow rate. For flow rates higher than this optimal, the high oxygen concentration led to growth inhibition and for lower flow rates growth limitations occur due to insufficient oxygen supply. Because of the nonlinear effects of the autocatalytic substrate inhibition growth kinetics coupled to the convective transport, the rate of growth at this optimal flow rate is higher than that in a corresponding well-mixed reactor where oxygen concentration is set at the maximum indicated by the inhibitory kinetics. ©2005 Wiley Periodicals, Inc. [source] | |||||||||||||||||||