Straightforward Assumption Research Articles

Land Fraction Diversity on Earth-like Planets and Implications for Their Habitability.

A balanced ratio of ocean to land is believed to be essential for an Earth-like biosphere, and one may conjecture that plate-tectonics planets should be similar in geological properties. After all, the volume of continental crust evolves toward an equilibrium between production and erosion. If the interior thermal states of Earth-sized exoplanets are similar to those of Earth-a straightforward assumption due to the temperature dependence of mantle viscosity-one might expect a similar equilibrium between continental production and erosion to establish, and hence a similar land fraction. We show that this conjecture is not likely to be true. Positive feedback associated with the coupled mantle water-continental crust cycle may rather lead to a manifold of three possible planets, depending on their early history: a land planet, an ocean planet, and a balanced Earth-like planet. In addition, thermal blanketing of the interior by the continents enhances the sensitivity of continental growth to its history and, eventually, to initial conditions. Much of the blanketing effect is, however, compensated by mantle depletion in radioactive elements. A model of the long-term carbonate-silicate cycle shows the land and the ocean planets to differ by about 5 K in average surface temperature. A larger continental surface fraction results both in higher weathering rates and enhanced outgassing, partly compensating each other. Still, the land planet is expected to have a substantially dryer, colder, and harsher climate possibly with extended cold deserts in comparison with the ocean planet and with the present-day Earth. Using a model of balancing water availability and nutrients from continental crust weathering, we find the bioproductivity and the biomass of both the land and ocean planets to be reduced by a third to half of those of Earth. The biosphere on these planets might not be substantial enough to produce a supply of free oxygen.

Vehicle Dynamics and Train-Induced Ground Vibration—Theoretical Analyses and Simultaneous Vehicle, Track, and Soil Measurements

Ground vibrations near railway lines are generated by the forces that are acting between wheel and rail. It seems to be a straight forward assumption that the vehicle dynamics are important for the level and the frequencies of the excitation forces. Different vehicle dynamics phenomena are analysed for their role in the excitation of ground vibrations: rigid body modes of the bogies, elastic (bending) modes of the car body, and elastic modes of the wheelset. The theoretical analyses use rigid body models, simplified elastic models, and detailed elastic models. Some of these problems are vehicle–track interaction problems where 3D finite-element boundary-element models have been used for the track and soil. It is shown that the rigid or flexible vehicle modes are well in the frequency range of ground vibrations (4 to 100 Hz). They have an influence on the excitation force but the additional forces are rather small and can be neglected in ground vibration prediction. The theoretical results are checked by experimental results of a simultaneous measurement of vehicle, track, and ground vibrations.

Lexical Planning in People Who Stutter: A Defect in Lexical Encoding or the Planning Scope?

Developmental stuttering is a widely discussed speech fluency disorder. Research on its mechanism has focused on an atypical interface between the planning (PLAN) and execution (EX) processes, known collectively as the EXPLAN model. However, it remains unclear how this atypical interface influences people who stutter. A straightforward assumption is that stuttering speakers adopt a smaller scope of speech planning, whereas a defect in word retrieval can be confounding. To shed light on this issue, we took the semantic blocking effect as an index to examine lexical planning in word and phrase production. In Experiment 1, for word production, pictures from the same semantic category were combined to form homogeneous blocks, and pictures from different categories were combined to form heterogeneous blocks. A typical effect of semantic blocking showing longer naming latencies for homogeneous blocks than heterogeneous ones was observed for both stuttering and fluent speakers. However, this effect was smaller for stuttering speakers, when it was subject to lexical defects in stuttering. In Experiment 2, for a conjoined noun phrase production task, the pictures referring to the first noun were manipulated into homogeneous and heterogeneous conditions. The semantic blocking effect was also much smaller for stuttering speakers, indicating a smaller scope of lexical planning. Therefore, the results provided more evidence in support of the EXPLAN model and indicated that a smaller scope of lexical planning rather than lexical defects causes the atypical interface for stuttering. Moreover, a comparison between these two tasks showed that the study findings have implications for syntactic defects in stuttering.

Gendered Violence as Revelation in John le Carré’s <em>The Night Manager</em>

Gendered Violence as Revelation in John le Carré’s <em>The Night Manager</em>

Depth Penetration and Scope Extension of Failures in the Cascading of Multilayer Networks

Real-world complex systems always interact with each other, which causes these systems to collapse in an avalanche or cascading manner in the case of random failures or malicious attacks. The robustness of multilayer networks has attracted great interest, where the modeling and theoretical studies of which always rely on the concept of multilayer networks and percolation methods. A straightforward and tacit assumption is that the interdependence across network layers is strong, which means that a node will fail entirely with the removal of all links if one of its interdependent nodes in other network layers fails. However, this oversimplification cannot describe the general form of interactions across the network layers in a real-world multilayer system. In this paper, we reveal the nature of the avalanche disintegration of general multilayer networks with arbitrary interdependency strength across network layers. Specifically, we identify that the avalanche process of the whole system can essentially be decomposed into two microscopic cascading dynamics in terms of the propagation direction of the failures: depth penetration and scope extension. In the process of depth penetration, the failures propagate from layer to layer, where the greater the number of failed nodes is, the greater is the destructive power that will emerge in an interdependency group. In the process of scope extension, failures propagate with the removal of connections in each network layer. Under the synergy of the two processes, we find that the percolation transition of the system can be discontinuous or continuous with changes in the interdependency strength across network layers, which means that a sudden system-wide collapse can be avoided by controlling the interdependency strength across network layers. Our work not only reveals the microscopic mechanism of global collapse in multilayer infrastructure systems but also provides stimulating ideas on intervention programs and approaches for cascade failures.

Neural imaginaries at work: Exploring Australian addiction treatment providers' selective representations of the brain in clinical practice.

Although addiction neuroscience hopes to uncover the neural basis of addiction and deliver a wide range of novel neuro-interventions to improve the treatment of addiction, the translation of addiction neuroscience to practice has been widely viewed as a ‘bench to bedside’ failure. Importantly, though, this linear ‘bench to bedside’ conceptualisation of knowledge translation has not been attentive to the role addiction treatment providers play in reproducing, translating, or resisting neuroscientific knowledge. This study explores how, to what extent, and for what purpose addiction treatment providers deploy neuroscientific representations and discuss the brain in practice. It draws upon interviews with 20 Australian treatment providers, ranging from addiction psychiatrists in clinics to case-workers in therapeutic communities. Our findings elucidate how different treatment providers: (1) invoke the authority and make use of neuroscience in practice (2) make reference to neuroscientific concepts (e.g., neuroplasticity); and sometimes represent the brain using vivid neurobiological language, metaphors, and stories; and, (3) question the therapeutic benefits of discussing neuroscience and the use of neuroimages with clients. We argue that neurological ontologies of addiction, whilst shown to be selectively and strategically invoked in certain circumstances, may also at times be positioned as lacking centrality and salience within clinical work. In doing so, we render problematic any straightforward assumption about the universal import of neuroscience to practice that underpins narratives of ‘bench to bedside’ translation.

Natural Sesquiterpene Lactones of the 4,15-iso-Atriplicolide Type are Inhibitors of Trypanothione Reductase.

In the course of our investigations on the antitrypanosomal potential of sesquiterpene lactones (STL), we have recently reported on the exceptionally strong activity of 4,15-iso-Atriplicolide tiglate, which demonstrated an IC50 value of 15 nM against Trypanosoma brucei rhodesiense, the etiologic agent responsible for East African human trypanosomiasis (HAT). Since STLs are known to often interact with their biological targets (e.g., in anti-inflammatory and anti-tumor activity) by means of the covalent modification of biological nucleophiles—most prominently free cysteine thiol groups in proteins—it was a straightforward assumption that such compounds might interfere with the trypanothione-associated detoxification system of trypanosomes. This system heavily relies on thiol groups in the form of the dithiol trypanothione (T(SH)2) and in the active centers of enzymes involved in trypanothione metabolism and homeostasis. Indeed, we found in the present study that 4,15-iso-atriplicolide tiglate, as well as its structural homologues, the corresponding methacrylate and isobutyrate, are inhibitors of trypanothione reductase (TR), the enzyme serving the parasites to keep T(SH)2 in the dithiol state. The TR inhibitory activity was demonstrated to be time-dependent and irreversible. Quite interestingly, of the several further STLs with different core structures that were also tested, none inhibited TR at a significant level. Thus, the TR inhibitory effect by the 4,15-iso-atriplicolide esters appears to be specific for this particular type of furanoheliangolide-type STL. Some structure–activity relationships can already be deduced on the basis of the data reported here, which may serve as the starting point for searching further, possibly more potent, TR inhibitors.

Reflections on Conversations and Memory.

The study of memory and remembering has traditionally either stripped meaning away from acts of remembering to reveal the "raw material of memory" or explored how meaning guides the reconstruction of the past. In reflecting on the contributions to this topic, there appears to be an emerging "third-way," which holds that there is an inextricable relation between conversations and remembering. The articles in this volume exemplify how conversing is often an act of remembering and represent approaches to memory that might not otherwise be taken if one were to study memory as a within-individual phenomenon. The implications of this approach are far-ranging and present the opportunity to pose new questions about the nature of remembering as it unfolds in conversation. The contributing articles have expanded the scope of what memory researchers can study by adopting a relatively straightforward assumption about the sociality of remembering and the role of the conversation in the social process.

Introduction: Fraud and Forgery in Victorian Culture

Introduction: Fraud and Forgery in Victorian Culture Elly McCausland (bio) and Jakob Gaardbo Nielsen (bio) In one of the central passages of Anthony Trollope’s novel The Way We Live Now (1875), the reader accompanies Augustus Melmotte, megalomaniac financier, into his private office and watches this “tower of strength” (72) and “prophet” (331) of commercial enterprise forge the signatures of his daughter and his clerk on a transfer deed. The rich and politically ambitious railway magnate has placed a large fortune in his daughter’s name so as to keep it from “the ordinary fluctuations of commercial enterprise” (579). Now, with a ruined reputation and in need of liquid funds in an avalanching stock market, and faced with his daughter’s refusal to sanction the transfer in writing, Melmotte “[practices] the two signatures for the best part of an hour” (585) before setting off into the City with the forged documents. Despite his meticulous rehearsing, however, Melmotte misses one of the signature lines, leaving the whole thing void—a fact the narrator later ironically takes to mean that “any fool might do an honest business,” while “fraud requires a man to be alive and wide awake at every turn!” (619). As the reader knows at this point in the novel, Melmotte is himself also a fraud: a serial forger of identities circulating between European capitals. In an interior monologue, the narrator discloses that “Fraud and dishonesty had been the very principle of his life” (613). Melmotte’s lack of a traceable origin troubles his biographers, who, after his suicide, interestingly conclude that he was in fact the son of “a noted coiner in New York” (735). The association with the profession of coining doubles the impression that his identity is reproductive, imitative, and ultimately counterfeit. His signatures, then, are false in a double sense: they are not his own, and they are issued by a body that does not belong to a single identity. Much like the bastard or the impostor, the forger is something of an emblem of the Victorian imagination. In an epistemological system characterized by shifting attitudes toward the act of seeing—a system in which “the sufficiency of the visible” (Flint 25) and the ability of the visible to function as a “[way] of knowing” (Malton 6) were being challenged on several fronts—forgeries of this kind were, as Sara Malton has argued, an “intensely dangerous social and economic disruption” (2). A signature is a quintessentially “authentic” inscription of identity upon a document that becomes legitimate only at the moment of inscription. It is a fixed mark whose stasis belies the performative nature of its inscription, converting [End Page 227] blank potential into supposedly robust legitimacy and authority. The forgery of a signature—its unsanctioned appearance out of another hand—seems therefore almost sacrilegious. It violates a whole system of identification, a logic of origination and authenticity, the cohesion of moral selfhood, and the concept of the self-contained subject. Echoing Derrida’s notion of the circular nature of exchange, Malton likens the false signature to a false coin insofar as it claims for itself “an authorized origin” (14) that, firstly, it does not have, and, secondly and more paradoxically, is inherently difficult to verify “because of its very similarity to the mechanism of credit it exploits” (14). Similarly, the muteness of the forged words in a false signature, their inability to identify themselves as anything other than real, at once mimics and undermines the function of trust in industrial commercial society. In literary and philosophical texts, the forged signature and the false coin not only symbolize the insecurity of modern systems of exchange but also give expression to a crisis of subjectivity and representation. Concurrently, acts of fraud and forgery can have empowering or assertive qualities. The belief that names and signatures belong to singular individuals, that faces and identities signify or embody each other, that one person is not another, that identity is more than an assemblage of contingent truth claims, has never been a straightforward assumption and leaves room for the poet as well as the forger. In his landmark study of literary forgery, Nick Groom stresses the necessity of embracing forgery...

Azathioprine-induced interstitial nephritis in an anti-neutrophil cytoplasmic antibody (ANCA) myeloperoxidase (MPO) vasculitis patient.

Azathioprine (AZA) is used in a wide array of autoimmune diseases, still corresponding to the mainstay maintenance therapy in anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides. Although generally well-tolerated, several side effects are recognized. We report the case of a 50-year-old Caucasian man with kidney-limited ANCA myeloperoxidase (MPO) vasculitis who presented with general malaise, fever, worsening renal function, and elevated inflammatory markers 2 weeks after the initiation of therapy with oral AZA. Although a disease relapse was suspected, renal biopsy revealed an eosinophilic infiltrate, suggestive of acute interstitial nephritis. After suspension of AZA, a sustained improvement of renal function and normalization of inflammatory markers was observed. A diagnosis of allergic interstitial nephritis secondary to AZA was established, corresponding to the first biopsy-proven case described in an ANCA MPO vasculitis patient. Although rare, renal toxicity of AZA must be present in the clinician's mind, avoiding the straightforward assumption of disease relapse in the case of worsening renal function.

The Influence of Sacred Beliefs in Environmental Risk Perception and Attitudes

Elements of the natural world, such as mountains, rivers, and forests, are often seen as sacred in many cultural traditions. Recent conservation movements have even begun to draw on spiritual and religious beliefs to promote issues of environmental sustainability. The straightforward assumption in these cases is that sacred beliefs (compared with secular ones) will hold greater sway in alerting people to various environmental perils. However, environmental risk perception is a complex process, and we find that, in some cases, viewing natural resources as sacred may lead to a diminished perception of environmental risks such as pollution. Across three studies, we show that sacred beliefs may inure participants to the harmful effects of pollution in the Ganges River. Implications of these sacred value–based risk perceptions for conservation movements are discussed.

Looking for Links: How Faculty Research Productivity Correlates with Library Investment and Why Electronic Library Materials Matter Most

Abstract
 
 Objective – This paper summarizes two studies that share the same research question: do universities produce more scholarly research when they invest more in their libraries? Research libraries spend a great deal of effort reporting their expenditures, collections statistics, and other measures that serve as a basis for interlibrary comparison and even rankings. The straightforward assumption implied by this activity is that libraries better serve their student and research communities when they are well-funded and well-resourced. The studies examined here both ask if that notion can be validated empirically, not because research libraries require some sort of justification, but because in an environment of tough budget decisions and shifting opinions about the changing role of libraries, it may be useful to demonstrate that sustained investment in libraries offers tangible returns or that the failure to do so can result in tangible costs.
 
 Methods – A cross-sectional design featuring ordinary least squares regression analysis was used in both studies to estimate the relationship between scholarly research productivity at U.S. doctoral institutions and an array of institutional characteristics presumed to influence that productivity. The concept of research productivity is operationalized as the total number of scholarly journal articles produced by each institution over a five year period – as journal articles represent the most common form of scholarly expression across the greatest number of academic fields. Serving as the dependent variable, this data was regressed against a variety of institutional characteristics including faculty size, research expenditures, and grant awards, and several library variables centered mostly on expenditures. The concept behind this design is that to realistically explore the relationship between levels of library investment and research productivity, all other institutional drivers of research productivity must also be represented in the dataset. While the design was similar for both studies, they each drew on different data sources and marginally different populations. 
 
 Results – Both studies found that an institution’s research productivity is positively and significantly correlated with the level of investment it makes in its libraries. Furthermore, both studies found electronic library material expenditures to be particularly associated with increased productivity. This relationship was so strong that an institution’s level of research productivity appears to be sensitive to how its library’s collection budget is allocated between print and electronic materials. As the portion of the budget dedicated to non-electronic material grew, research productivity decreased in statistically significant fashion in both studies.
 
 Conclusion – While both studies succeeded in demonstrating the existence of an empirical relationship between library investment and research productivity, the most intriguing finding is that both studies observed a decrease in number of journal articles being produced as expenditures for non-electronic library materials increased. The conclusion is that the efficiencies of electronic resources offer such advantages over the use of traditional library materials in supporting scholarly research that productivity suffers as institutions dedicate a greater portion of their collection budgets to print materials at the expense of electronic materials.

A Note on the Existence of Nonsmooth Nonconvex Optimization Problems

Sufficient conditions for the existence of a solution to an abstract optimization problem in Banach spaces are given, which do not rely on convexity, regularity properties or a straightforward coerciveness assumption. Applications to sparsity-constrained optimization and to problems from mechanics are provided.

Najboljši ali lažni prijatelji? Luščenje slovensko-hrvaških prevodnih ustreznic in lažnih prijateljev iz korpusov

V prispevku predstavimo korpusni pristop k samodejnemu luščenju prevodnih ustreznic in lažnih prijateljev med slovenščino in hrvaščino. Pristop izkorišča ortografske podobnosti med jezikoma in temelji na predpostavki distribucijske semantike, ki se glasi, da govorci obeh jezikov besede s podobnim pomenom uporabljamo v podobnih kontekstih. To nam po eni strani omogoča hitro izgradnjo slovensko-hrvaškega dvojezičnega leksikona, za katero razen primerljivih spletnih korpusov ne potrebujemo nobenega drugega vira znanja. Po drugi strani pa lahko na podlagi iste predpostavke s pomočjo korpusnih podatkov prepoznamo tiste sorodnice, ki so si podobne zgolj površinsko, leksikalizirajo pa različne pojme in se zato tudi različno uporabljajo. Predstavljen pristop je jezikovno neodvisen, zaradi česar je privlačen za številna področja računalniške obdelave naravnega jezika, kjer še vedno vlada veliko pomanjkanje leksikalnih virov, njihove ročne izdelave pa si ne moremo privoščiti. Pristop je prav tako zelo koristen v leksikografiji in za poučevanje tujih jezikov, saj nam pomaga osvetliti leksikalne posebnosti za določen jezikovni par oziroma strokovno področje.

Reading English with Japanese in mind: Effects of frequency, phonology, and meaning in different-script bilinguals

Previous priming studies suggest that, even for bilinguals of languages with different scripts, non-selective lexical activation arises. This lexical decision eye-tracking study examined contributions of frequency, phonology, and meaning of L1 Japanese words on L2 English word lexical decision processes, using mixed-effects regression modeling. The response times and eye fixation durations of late bilinguals were co-determined by L1 Japanese word frequency and cross-language phonological and semantic similarities, but not by a dichotomous factor encoding cognate status. These effects were not observed for native monolingual readers and were confirmed to be genuine bilingual effects. The results are discussed based on the Bilingual Interactive Activation model (BIA+, Dijkstra & Van Heuven, 2002) under the straightforward assumption that English letter units do not project onto Japanese word units.

The Bow and Cultural Complexity of the Canadian Plains

The timing and circumstances of the introduction of the bow and arrow into past North American economic and social lifeways have been sources of interest and controversy among archeologists for a very long time. Initial interpretations of the adoption of the bow and arrow generally seem to have been based on the rather straightforward assumption of functional superiority as a hunting tool. That is, the bow and arrow was simply a better instrument than the atlatl-dart technology it replaced. More recently, however, researchers exploring the effectiveness of the atlatl as a hunting tool have responded with studies that challenge the assumed universal functional superiority of the bow and arrow as a hunting device. Social coercion and warfare theory presents an alternative perspective on the adoption of the bow and arrow.

Anxiety and technological change — Explaining the inverted U-curve of sulphur dioxide emissions in late 20th century Finland

This article examines the linkage between per capita GDP and sulphur dioxide emissions for one single country, in this case Finland. The narrow approach together with a combination of a historical and economical approach enables us to cut deeper into the controversial environmental Kuznets curve-hypothesis. We found the main reasons for a downturn in sulphur emissions to be: technological development and anxiety about possible environmental damage and economic costs related to that. It can be discussed whether our results refute the environmental Kuznets curve or just show possible ways in which the environmental Kuznets curve is achieved. Nevertheless our case study casts some serious doubt on the most straightforward assumption coming out from the EKC, that economic growth would automatically solve environmental problems. We claim that the causal connection might also go in an opposite direction: proper environmental standards and conservation comprise a necessary condition for economic growth in the long run.

Tousled kinase TLK1B mediates chromatin assembly in conjunction with Asf1 regardless of its kinase activity

BackgroundThe Tousled Like Kinases (TLKs) are involved in chromatin dynamics, including DNA replication and repair, transcription, and chromosome segregation. Indeed, the first two TLK1 substrates were identified as the histone H3 and Asf1 (a histone H3/H4 chaperone), which immediately suggested a function in chromatin remodeling. However, despite the straightforward assumption that TLK1 acts simply by phosphorylating its substrates and hence modifying their activity, TLK1 also acts as a chaperone. In fact, a kinase-dead (KD) mutant of TLK1B is functional in stimulating chromatin assembly in vitro. However, subtle effects of Asf1 phosphorylation are more difficult to probe in chromatin assembly assays. Not until very recently was the Asf1 site phosphorylated by TLK1 identified. This has allowed for probing directly the functionality of a site-directed mutant of Asf1 in chromatin assembly assays.FindingsAddition of either wt or non-phosphorylatable mutant Asf1 to nuclear extract stimulates chromatin assembly on a plasmid. Similarly, TLK1B-KD stimulates chromatin assembly and it synergizes in reactions with supplemental Asf1 (wt or non-phosphorylatable mutant).ConclusionsAlthough the actual function of TLKs as mediators of Asf1 activity cannot be easily studied in vivo, particularly since in mammalian cells there are two TLK genes and two Asf1 genes, we were able to study specifically the stimulation of chromatin assembly in vitro. In such assays, clearly the TLK1 kinase activity was not critical, as neither a non-phosphorylatable Asf1 nor use of the TLK1B-KD impaired the stimulation of nucleosome formation.

Diminished plasticity of visual function and sensory maps after cortical stroke in mice

Event Abstract Back to Event Diminished plasticity of visual function and sensory maps after cortical stroke in mice Franziska Greifzu1*, Silvio Schmidt2, Friedrich Schmidt1, Otto W. Witte2 and Siegrid Löwel1 1 Friedrich-Schiller-University, Germany 2 University of Jena Medical School, Germany Stroke is a major cause of death and disability in the industrialized countries. It is an encouraging observation that clinically most patients who do suffer from stroke recover to some degree from the deficits which they incur. The most straightforward assumption is usually that this is due to plasticity. Many in vitro studies indicated that there is an increased plasticity in the perilesional zone of cortical infarcts. In the present study we investigated in vivo the impact of a photothrombotically induced cortical stroke on the plasticity of the neighbouring visual cortex after short periods of monocular deprivation (MD). Visual function was analyzed behaviourally with a virtual optomotor system. In addition, visual cortical maps were recorded using intrinsic signal optical imaging. After 7 days of MD, control animals showed a significant enhancement of visual acuity in the non-deprived eye and a significant ocular dominance shift towards the open eye in the optical imaging experiments. In contrast, in animals with a cortical stroke, both the enhancement of visual acuity and the ocular dominance shift were significantly lower. Thus our in vivo data rather indicate that neuronal plasticity is diminished in the surround of a cortical infarct. Conference: Bernstein Symposium 2008, Munich, Germany, 8 Oct - 10 Oct, 2008. Presentation Type: Poster Presentation Topic: All Abstracts Citation: Greifzu F, Schmidt S, Schmidt F, Witte OW and Löwel S (2008). Diminished plasticity of visual function and sensory maps after cortical stroke in mice. Front. Comput. Neurosci. Conference Abstract: Bernstein Symposium 2008. doi: 10.3389/conf.neuro.10.2008.01.052 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 14 Nov 2008; Published Online: 14 Nov 2008. * Correspondence: Franziska Greifzu, Friedrich-Schiller-University, Jena, Germany, Franziska.Greifzu@uni-jena.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Franziska Greifzu Silvio Schmidt Friedrich Schmidt Otto W Witte Siegrid Löwel Google Franziska Greifzu Silvio Schmidt Friedrich Schmidt Otto W Witte Siegrid Löwel Google Scholar Franziska Greifzu Silvio Schmidt Friedrich Schmidt Otto W Witte Siegrid Löwel PubMed Franziska Greifzu Silvio Schmidt Friedrich Schmidt Otto W Witte Siegrid Löwel Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Adenine and adenosine salvage pathways in erythrocytes and the role of S‐adenosylhomocysteine hydrolase

This article is devoted to the study of redundancy and yield of salvage pathways in human erythrocytes. These cells are not able to synthesize ATP de novo. However, the salvage (recycling) of certain nucleosides or bases to give nucleotide triphosphates is operative. As the salvage pathways use enzymes consuming ATP as well as enzymes producing ATP, it is not easy to see whether a net synthesis of ATP is possible. As for pathways using adenosine, a straightforward assumption is that these pathways start with adenosine kinase. However, a pathway bypassing this enzyme and using S-adenosylhomocysteine hydrolase instead was reported. So far, this route has not been analysed in detail. Using the concept of elementary flux modes, we investigate theoretically which salvage pathways exist in erythrocytes, which enzymes belong to each of these and what relative fluxes these enzymes carry. Here, we compute the net overall stoichiometry of ATP build-up from the recycled substrates and show that the network has considerable redundancy. For example, four different pathways of adenine salvage and 12 different pathways of adenosine salvage are obtained. They give different ATP/glucose yields, the highest being 3:10 for adenine salvage and 2:3 for adenosine salvage provided that adenosine is not used as an energy source. Implications for enzyme deficiencies are discussed.