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Biological transport processes and space dimension.

Nadler, W; Stein, D L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/08/1991 EN
Relevância na Pesquisa
45.8%
We discuss the generic time behavior of reaction-diffusion processes capable of modeling various types of biological transport processes, such as ligand migration in proteins and gating fluctuations in ion channel proteins. The main observable in these two cases, the fraction of unbound ligands and the probability of finding the channel in the closed state, respectively, exhibits an algebraic t-1/2 decay at intermediate times, followed by an exponential cutoff. We provide a simple framework for understanding these observations and explain their ubiquity by showing that these qualitative results are independent of space dimension. We also derive an experimental criterion to distinguish between a one-dimensional process and one whose effective dimension is higher.

The Kinetics of Selective Biological Transport: III. Erythrocyte-Monosaccharide Transport Data

Miller, D. M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1968 EN
Relevância na Pesquisa
45.86%
The simplest biological transport system so far extensively investigated is that of monosaccharides in human erythrocytes. Despite its simplicity there is still considerable doubt and divergence of opinion concerning its mechanism. Some confusion may arise as a result of the comparison of diverse data obtained by different workers using a variety of experimental techniques. To minimize this problem, an attempt is made here to repeat, under standard conditions and with as much care as possible, five of the more definitive types of experiments previously performed on this system. It is hoped that the result of this effort is an internally consistent set of data with which the quantitative predictions of various proposed mechanisms may be compared as a primary criterion for their acceptability.

Thermal Migration in Biological Transport?

Davies, Martin
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1965 EN
Relevância na Pesquisa
45.8%
It is shown by thermodynamic arguments and by semiquantitative considerations that the contribution of thermal migration to biological transport is likely to be small.

Intra-Protein Interactions Across a Fluid Membrane as a Model for Biological Transport

Stein, W. D.
Fonte: The Rockefeller University Press Publicador: The Rockefeller University Press
Tipo: Artigo de Revista Científica
Publicado em 01/07/1969 EN
Relevância na Pesquisa
45.76%
A model is proposed for the mechanism of action of the glucose transport system of the human erythrocyte. The model is based on the possibility of there being interaction through the membrane between superficially disposed protein subunits, these units being embedded within the bimolecular lipid layer, anchored to the aqueous phase, perhaps mobile in the plane of each face of the membrane. The subunits have the ability to bind sugar and, when associated with the symmetrical protein at the opposite face of the membrane, transfer sugar across the membrane. Evidence for the model is presented. The possibility that this model may also be a model for the cell membrane as such is briefly touched upon.

Comparison of two measures of PSI electron transport in winter rye

Chapman, B. Patrick.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
45.85%
The number of P700 (the reaction centre of Photosystem I) converted to P700+, in winter rye, was determined by measuring the absorbance change at 820nm . It was found, with a single turnover flash, that thylakoids isolated from cold grown plants have a 50% greater number of P700 oxidized than thylakoids isolated from warm grown plants. Incubation of thylakoids in the dark at 35 C did not change the number of P700 oxidized. The conversion of P700 to P700+ with a single flash can be compared to a steady state rate of electron transport using a Clark electrode. The results for P700 oxidation using the absorbance change at 820 nm measure effects within the PSI complex whereas the results obtained from a Clark electrode measures steady state electron transport between the cytochrome blf complex and the PSI complex. In contrast to the results for P700 oxidation it was shown, using a Clark electrode, that both thylakoids from cold grown plants and thylakoids incubated at in the dark 35 C exhibited 50% higher rates of electron transport than thylakoids from warm grown plants. The correlation between the higher rate of steady state PSI electron transport observed in thylakoids isolated from cold grown winter rye and number of active PSI reaction centres localizes the site of the increase to the PSI reaction centre. In contrast the lack of correlation after incubation at 35 C indicates the increase in the rate of light saturated electron transport in thylakoids isolated from cold grown plants and thylakoids incubated in the dark at 35 C occur by different mechanisms.

Determination of in vivo absorption, metabolism, and transport of drugs by the human intestinal wall and liver with a novel perfusion technique

von Richter, O.; Greiner, B.; Fromm, M.; Fraser, R.; Omari, T.; Barclay, M.; Dent, J.; Somogyi, A.; Eichelbaum, M.
Fonte: Mosby Inc Publicador: Mosby Inc
Tipo: Artigo de Revista Científica
Publicado em //2001 EN
Relevância na Pesquisa
45.9%
Background and Aims: The contribution of the gastrointestinal tract in comparison with the liver for the low and variable bioavailability of orally administered drugs is still poorly understood. Here we report on a new intestinal perfusion technique for the direct assessment of absorption, metabolism, and transport of drugs by the intestinal wall. Methods: In 6 healthy volunteers a multilumen perfusion catheter was used to generate a 20-cm isolated jejunal segment that was perfused with 80 mg verapamil. Simultaneously, 5 mg [2H7]verapamil was given intravenously. Blood, perfusate, and bile samples were analyzed for parent verapamil and its major metabolites. Results: The mean fraction of the verapamil dose absorbed from the 20-cm segment was 0.76 but substantial interindividual variability (0.51-0.96) was shown. Bioavailability was low (19.3%). The intestinal wall contributed to the same extent as the liver to extensive first-pass metabolism (mean extraction ratio, 0.49 versus 0.48). Substantial transport of verapamil metabolites from the systemic circulation via the enterocytes into the intestinal lumen was observed. Compared with biliary excretion, intestinal secretion into a 20-cm jejunal segment contributed to drug elimination to a similar extent. Conclusion: First-pass metabolism by the intestinal wall is extensive and contributes to the same extent as the liver to low bioavailability of some drugs such as verapamil. Moreover...

Early treatment of the pregnant guinea pig with IGFs promotes placental transport and nutrient partitioning near term

Sferruzzi-Perri, A.; Owens, J.; Standen, P.; Taylor, R.; Heinemann, G.; Robinson, J.; Roberts, C.
Fonte: Amer Physiological Soc Publicador: Amer Physiological Soc
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
45.79%
Appropriate partitioning of nutrients between the mother and conceptus is a major determinant of pregnancy success, with placental transfer playing a key role. Insulin-like growth factors (IGFs) increase in the maternal circulation during early pregnancy and are predictive of fetal and placental growth. We have previously shown in the guinea pig that increasing maternal IGF abundance in early to midpregnancy enhances fetal growth and viability near term. We now show that this treatment promotes placental transport to the fetus, fetal substrate utilization, and nutrient partitioning near term. Pregnant guinea pigs were infused with IGF-I, IGF-II (both 1 mg·kg–1·day–1) or vehicle subcutaneously from days 20–38 of pregnancy (term = 69 days). Tissue uptake and placental transfer of the nonmetabolizable radio analogs [3H]methyl-D-glucose (MG) and [14C]aminoisobutyric acid (AIB) in vivo was measured on day 62. Early pregnancy exposure to elevated maternal IGF-I increased placental MG uptake by >70% (P = 0.004), whereas each IGF increased fetal plasma MG concentrations by 40–50% (P < 0.012). Both IGFs increased fetal tissue MG uptake (P < 0.048), whereas IGF-I also increased AIB uptake by visceral organs (P = 0.046). In the mother...

Ammonia and amino acid transport across symbiotic membranes in nitrogen-fixing legume nodules

Day, D.; Poole, P.; Tyerman, S.; Rosendahl, L.
Fonte: Birkhauser Verlag Ag Publicador: Birkhauser Verlag Ag
Tipo: Artigo de Revista Científica
Publicado em //2001 EN
Relevância na Pesquisa
45.92%
Biological nitrogen fixation involves the reduction of atmospheric N2 to ammonia by the bacterial enzyme nitrogenase. In legume-rhizobium symbioses, the nitrogenase-producing bacteria (bacteroids) are contained in the infected cells of root nodules within which they are enclosed by a plant membrane to form a structure known as the symbiosome. The plant provides reduced carbon to the bacteroids in exchange for fixed nitrogen, which is exported to the rest of the plant. This exchange is controlled by plant-synthesised transport proteins on the symbiosome membranes. This review summarises our current understanding of these transport processes, focusing on ammonia and amino acid transport.; The original publication can be found at www.springerlink.com

Shoot Na+ exclusion and increased salinity tolerance engineered by cell type-specific alteration of Na+ transport in arabidopsis

Moller, I.; Gilliham, M.; Jha, D.; Mayo, G.; Roy, S.; Coates, J.; Haseloff, J.; Tester, M.
Fonte: Amer Soc Plant Physiologists Publicador: Amer Soc Plant Physiologists
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
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45.82%
Soil salinity affects large areas of cultivated land, causing significant reductions in crop yield globally. The Na+ toxicity of many crop plants is correlated with overaccumulation of Na+ in the shoot. We have previously suggested that the engineering of Na+ exclusion from the shoot could be achieved through an alteration of plasma membrane Na+ transport processes in the root, if these alterations were cell type specific. Here, it is shown that expression of the Na+ transporter HKT1;1 in the mature root stele of Arabidopsis thaliana decreases Na+ accumulation in the shoot by 37 to 64%. The expression of HKT1;1 specifically in the mature root stele is achieved using an enhancer trap expression system for specific and strong overexpression. The effect in the shoot is caused by the increased influx, mediated by HKT1;1, of Na+ into stelar root cells, which is demonstrated in planta and leads to a reduction of root-to-shoot transfer of Na+. Plants with reduced shoot Na+ also have increased salinity tolerance. By contrast, plants constitutively expressing HKT1;1 driven by the cauliflower mosaic virus 35S promoter accumulated high shoot Na+ and grew poorly. Our results demonstrate that the modification of a specific Na+ transport process in specific cell types can reduce shoot Na+ accumulation...

Stimulation of Aquaporin-Mediated Fluid Transport by Cyclic GMP in Human Retinal Pigment Epithelium In Vitro

Baetz, N.; Stamer, W.; Yool, A.
Fonte: Assoc Research Vision Ophthalmology Inc Publicador: Assoc Research Vision Ophthalmology Inc
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
45.84%
PURPOSE: The retinal pigment epithelium (RPE) expresses aquaporin-1 (AQP1) and components of the natriuretic peptide signaling pathway. We hypothesized that stimulation of the natriuretic signaling pathway in RPE with atrial natriuretic peptide (ANP) and with membrane-permeable analogs of cGMP would induce a net apical-to-basal transport of fluid. METHODS: The hypothesis was tested using human RPE cultures that retain properties seen in vivo. Confluent monolayers were treated with ANP or membrane-permeable cGMP analogs in the presence of anantin, H-8, and an AQP1 inhibitor, AqB013. Fluid movement from the apical to basal chambers was measured by weight and used to calculate net fluid transport. RESULTS: Our results demonstrated a 40% increase in net apical-to-basal fluid transport by ANP (5 μM) that was inhibited completely by the ANP receptor antagonist anantin and a 60% increase in net apical-to-basal fluid transport in response to the extracellularly applied membrane-permeable cGMP analog pCPT-cGMP (50 μM), which was not affected by the protein kinase G inhibitor H-8. The aquaporin antagonist AqB013 (20 μM) inhibited the cGMP-stimulated RPE fluid flux. CONCLUSIONS: The effect of cGMP is consistent with an enhancement of the net fluid flux in RPE mediated by AQP1 channels. Pharmacologic activation of cGMP signaling and concomitant stimulation of fluid uptake from the subretinal space could offer insights into a new approach to treating or reducing the risk of retinal detachment.; Nicholas W. Baetz...

Spermidine biosynthesis and transport modulate pneumococcal autolysis

Potter, A.J.; Paton, J.C.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
Relevância na Pesquisa
45.76%
Polyamines are small cationic molecules that have far-reaching roles in biology. In the case of pathogenic bacteria, these functions include those central to their pathogenesis. Streptococcus pneumoniae is a major bacterial pathogen, causing a diverse range of diseases that account for significant morbidity and mortality worldwide. In this work, we characterize the polyamine biosynthetic pathway of S. pneumoniae, demonstrating that this organism produces spermidine from arginine. The synthesis of spermidine was found to be nonessential for growth in a polyamine-free chemically defined medium. However, mutant strains lacking the ability to synthesize or transport spermidine displayed a significant delay in the onset of autolysis. We provide evidence for a model in which spermidine modulates the activity of the major autolysin LytA in the pneumococcal cell wall compartment via interactions with negatively charged molecules, such as teichoic acids.; Adam J. Potter and James C. Paton; Published ahead of print 4 August 2014

Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH₄⁺ transport; Soybean SAT1 (Symbiotic Ammonium Transporter 1) encodes a bHLH transcription factor involved in nodule growth and NH(4)(+) transport

Chiasson, D.M.; Loughlin, P.C.; Mazurkiewicz, D.; Mohammadidehcheshmeh, M.; Fedorova, E.E.; Okamoto, M.; McLean, E.; Glass, A.D.M.; Smith, S.E.; Bisseling, T.; Tyerman, S.D.; Day, D.A.; Kaiser, B.N.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
Relevância na Pesquisa
45.84%
Glycine max symbiotic ammonium transporter 1 was first documented as a putative ammonium (NH4(+)) channel localized to the symbiosome membrane of soybean root nodules. We show that Glycine max symbiotic ammonium transporter 1 is actually a membrane-localized basic helix-loop-helix (bHLH) DNA-binding transcription factor now renamed Glycine max bHLH membrane 1 (GmbHLHm1). In yeast, GmbHLHm1 enters the nucleus and transcriptionally activates a unique plasma membrane NH4(+) channel Saccharomyces cerevisiae ammonium facilitator 1. Ammonium facilitator 1 homologs are present in soybean and other plant species, where they often share chromosomal microsynteny with bHLHm1 loci. GmbHLHm1 is important to the soybean rhizobium symbiosis because loss of activity results in a reduction of nodule fitness and growth. Transcriptional changes in nodules highlight downstream signaling pathways involving circadian clock regulation, nutrient transport, hormone signaling, and cell wall modification. Collectively, these results show that GmbHLHm1 influences nodule development and activity and is linked to a novel mechanism for NH4(+) transport common to both yeast and plants.; David M. Chiasson, Patrick C. Loughlin, Danielle Mazurkiewicz, Manijeh Mohammadidehcheshmeh...

Quantitative proteomics reveals that plasma membrane microdomains from poplar cell suspension cultures are enriched in markers of signal transduction, molecular transport, and callose biosynthesis

Srivastava, V.; Malm, E.; Sundqvis, G.; Bulone, V.
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
45.86%
The plasma membrane (PM) is a highly dynamic interface that contains detergent-resistant microdomains (DRMs). The aim of this work was to determine the main functions of such microdomains in poplar through a proteomic analysis using gel-based and solution (iTRAQ) approaches. A total of 80 proteins from a limited number of functional classes were found to be significantly enriched in DRM relative to PM. The enriched proteins are markers of signal transduction, molecular transport at the PM, or cell wall biosynthesis. Their intrinsic properties are presented and discussed together with the biological significance of their enrichment in DRM. Of particular importance is the significant and specific enrichment of several callose [(1 → 3)-β-glucan] synthase isoforms, whose catalytic activity represents a final response to stress, leading to the deposition of callose plugs at the surface of the PM. An integrated functional model that connects all DRM-enriched proteins identified is proposed. This report is the only quantitative analysis available to date of the protein composition of membrane microdomains from a tree species.; Vaibhav Srivastava, Erik Malm, Gustav Sundqvist, and Vincent Bulone

Theoretical investigation of biological transport: Asymmetric simple exclusion processes in two-channel systems

Pronina, Ekaterina
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
45.9%
Multi-particle non-equilibrium dynamics in two-channel biological transport systems is investigated theoretically within the framework of asymmetric simple exclusion processes (ASEP). In exclusion processes particles move along the lattice by hopping between neighboring sites that are vacant. We consider the systems with open boundaries, where particles enter the lattice on the entrance site and leave from the exit site with given rates. Four different ASEP models are studied. The first two models investigate interchannel coupling between parallel channels in a one-way transport system. The third model considers junction of two parallel tracks, while the last model investigates two-way transport system with narrow entrances with coupling on the boundaries. Theoretical investigation of these non-equilibrium systems reveal many interesting phenomena, such as unusual phase diagrams that contain up to seven stationary-state phases, localization of the domain wall in the bulk of the system, symmetry-breaking and strong interparticle correlation. Stationary phase diagrams, particle currents and bulk values of densities are calculated in a mean-field approximation for the systems in the thermodynamic limit. In addition, exact matrix product ansatz method and phenomenological domain-wall theory are applied to analyze dynamic properties. For several systems nearest-neighbour correlation and density distribution functions are computed and size-scaling effects are analyzed. Extensive Monte Carlo computer simulations are carried out for all systems to test predictions and they verify our theoretical results.

Theoretical investigation of biological transport processes using discrete state stochastic models and simulations

Uppulury, Venkata
Fonte: Universidade Rice Publicador: Universidade Rice
Relevância na Pesquisa
45.99%
Biological processes take place far away from equilibrium and are of interest to uncover the basic principles governing these phenomena. In this endeavor, molecular transport across channels and transport of cargos by molecular motors are studied. Functioning of a normal cell is contingent upon import of important biomolecules via narrow passage ways called ‘Channels’. Due to entropic barriers the incoming molecules often face hindrance to cross the channels successfully and reach specific locations inside cells. But in real systems the channels utilize special binding sites to accelerate this process. For a set of in-vitro experiments studying molecular flow across channels in presence of the special attractive binding sites, explicit analytical results are derived and they evince how modification of the free energy barrier could achieve quicker translocation; it has been shown that the nature of interactions between molecule and channel, their spatial distribution, strength of interactions and inter-molecular interactions in the channel all contribute to the complex process of translocation. In another study, cargo transport driven by molecular motors is studied. Cells utilize special enzyme molecules called ‘molecular motors’ that convert chemical energy into mechanical motion to transport cargos. Often multiple motors drive transport due to viscous nature of cell medium and other crowding effects in cells. In such systems the extent to which multiple motors share applied load and in turn how they influence the properties of the system is not well understood. From in-vitro measurements pertinent to well-defined structural assemblies and quantitative modeling treatments...

Stochastic Modeling and Simulations of Biological Transport

Das, Rahul Kumar
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 170 p.; application/pdf
ENG
Relevância na Pesquisa
46.01%
Biological transport is an essential phenomenon for the living systems. A mechanistic investigation of biological transport processes is highly important for the characterization of physiological and cellular events, the design and functioning of several biomedical devices and the development of new therapies. To investigate the physical-chemical details of this phenomenon, concerted efforts of both experiments and theory are necessary. Motor proteins constitute a major portion of the active transport in the living cell. However, the actual mechanism of how chemical energy is converted into their directed motion has still remained obscure. Recent experiments on motor proteins have been producing exciting results that have motivated theoretical studies. In order to provide deep insight onto motor protein's mechanochemical coupling we have used stochastic modeling based on discrete-state chemical kinetic model. Such models enable us to (1) resolve the contradiction between experimental observations on heterodimeric kinesins and highly popular hand-over-hand mechanism, (2) take into account the free energy landscape modification of individual motor domains due to interdomain interaction, (3) recognize the effect of spatial fluctuations on biochemical properties of molecular motors...

Effect of NaPi-mediated phosphate transport on intracellular pH

Moschen, I; Setiawan, Iwan; Broer, Stefan; Murer, H; Lang, Florian
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.79%
Extracellular pH has been shown previously to influence transport via type-II Na+/phosphate (NaPi) transporters by modifying the affinity of the carrier for Na+ and by altering the availability of divalent and monovalent phosphate. As the transport of mon

Amino acid permeases require COPII components and the ER resident membrane protein Shr3p for packaging into transport vesicles in vitro.

Kuehn, MJ; Schekman, R; Ljungdahl, PO
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Artigo de Revista Científica Formato: 585 - 595
Publicado em /11/1996 ENG
Relevância na Pesquisa
45.88%
In S. cerevisiae lacking SHR3, amino acid permeases specifically accumulate in membranes of the endoplasmic reticulum (ER) and fail to be transported to the plasma membrane. We examined the requirements of transport of the permeases from the ER to the Golgi in vitro. Addition of soluble COPII components (Sec23/24p, Sec13/31p, and Sar1p) to yeast membrane preparations generated vesicles containing the general amino acid permease. Gap1p, and the histidine permease, Hip1p. Shr3p was required for the packaging of Gap1p and Hip1p but was not itself incorporated into transport vesicles. In contrast, the packaging of the plasma membrane ATPase, Pma1p, and the soluble yeast pheromone precursor, glycosylated pro alpha factor, was independent of Shr3p. In addition, we show that integral membrane and soluble cargo colocalize in transport vesicles, indicating that different types of cargo are not segregated at an early step in secretion. Our data suggest that specific ancillary proteins in the ER membrane recruit subsets of integral membrane protein cargo into COPII transport vesicles.

Nuclear targeting signal recognistion: a key control point in nuclear transport?

Jans, David A; Xiao, Chong-Yun; Lam, Mark H C
Fonte: The Company of Biologists Ltd Publicador: The Company of Biologists Ltd
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.84%
Recent progress indicates that there are multiple pathways of nucleocytoplasmic transport which involve specific targeting sequences, such as nuclear localization sequences (NLSs), and cytosolic receptor molecules of the importin/karyopherin superfamily which recognise and dock the NLS-containing proteins at the nuclear pore. This first step of nuclear import/export is of central importance, with the affinity of the importin-targeting sequence interaction a critical parameter in determining transport efficiency. Different importins possess distinct NLS-binding specificities, which allows the system to be modulated through differential expression of the importins themselves, as well as through competition between different importins for the same protein, and between different proteins for the same importin. The targeting sequence-importin interaction can also be influenced directly by phosphorylation increasing the affinity of the interaction with importins or by targeting sequence masking through phosphorylation or specific protein binding. Targeting sequence recognition thus appears to represent a key control point in the regulation of nuclear transport. (C) 2000 John Wiley and Sons, Inc.

Hexose Transport in Asexual Stages of Plasmodium falciparum and Kinetoplastidae

Krishna, Sanjeev; Woodrow, C; Burchmore, R; Saliba, Kevin; Kirk, Kiaran
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
45.9%
The hexose sugar, glucose, is a vital energy source for most organisms and an essential nutrient for asexual stages of Plasmodium falciparum. Kinetoplastid organisms (eg. Trypanosoma and Leishmania spp) also require glucose at certain critical stages of their life cycles. Although phylogenetically unrelated, these organisms share many common challenges during the mammalian stages of a parasitic life cycle, and possess hexose uptake mechanisms that are amenable to study using similar methods. Defining hexose permeation pathways into parasites might expose an Achilles' heel at which both antidisease and antiparasite measures can be aimed. Understanding the mode of entry of glucose also presents a good general model for substrate acquisition in multicompartment systems. In this review, Sanjeev Krishna and colleagues summarize current understanding of hexose transport processes in P. falciparum and provide a comparison with data obtained from kinetoplastids.