Transport Of Organic Solutes Research Articles

Pressure sensing of lysosomes enables control of TFEB responses in macrophages.

Polymers are endocytosed and hydrolysed by lysosomal enzymes to generate transportable solutes. While the transport of diverse organic solutes across the plasma membrane is well studied, their necessary ongoing efflux from the endocytic fluid into the cytosol is poorly appreciated by comparison. Myeloid cells that employ specialized types of endocytosis, that is, phagocytosis and macropinocytosis, are highly dependent on such transport pathways to prevent the build-up of hydrostatic pressure that otherwise offsets lysosomal dynamics including vesiculation, tubulation and fission. Without undergoing rupture, we found that lysosomes incurring this pressure owing to defects in solute efflux, are unable to retain luminal Na+, which collapses its gradient with the cytosol. This cation 'leak' is mediated by pressure-sensitive channels resident to lysosomes and leads to the inhibition of mTORC1, which is normally activated by Na+-coupled amino acid transporters driven by the Na+ gradient. As a consequence, the transcription factors TFEB/TFE3 are made active in macrophages with distended lysosomes. In addition to their role in lysosomal biogenesis, TFEB/TFE3 activation causes the release of MCP-1/CCL2. In catabolically stressed tissues, defects in efflux of solutes from the endocytic pathway leads to increased monocyte recruitment. Here we propose that macrophages respond to a pressure-sensing pathway on lysosomes to orchestrate lysosomal biogenesis as well as myeloid cell recruitment.

Analytical solutions for transport of organic solutes in multi-layered porous media

In this study, analytical solutions for one-dimensional transport of organic solutes in multilayered porous media are developed using the methods of matrix transfer and variable separation, where multiple factors such as advection, diffusion, mechanical dispersion, adsorption, degradation, boundary condition type and change in concentration are systematically incorporated for the first time. Compared with the existing analytical solutions solved by the techniques of integral transformation or Laplace transformation, the approaches adopted in this paper are simpler and have a quicker convergence speed. Also, the proposed analytical solutions are more practical with clear expressions and consideration of multiple factors, which can be applied to various engineering cases such as bottom liner systems at landfills, covering systems of contaminated sediments and vertical barrier systems in contaminated sites. Furthermore, the correctness of the derived analytical solutions is effectively validated by comparison with the experimental results, as well as with the existing analytical solution and a numerical method. Following this, the effects of different factors on the transport process of a single organic solute in a five-layered medium are investigated, and some novel and vital laws are obtained. Overall, this research contributes to appropriate evaluation of the transport behaviours in multilayered porous media.

Improved Structural Stability of Charged Hydrogels under Organic CO2 Reduction Products: Effect of Acrylate and Methacrylate Backbone Linkages

Understanding the mixed solute transport behavior of CO2 reduction products (methanol and formate) in ion exchange membranes (IEMs) is of interest for CO2 reduction cells (CO2RCs). The role of an IEM in a typical CO2RC is to suppress the crossover of all CO2 reduction products while allowing the transport of electrolytes. Tuning the polymer rigidity of the membrane is a key contributor to such highly controlled transport of organic solutes in a dense hydrated membrane. Here, we investigate the mixed solute transport behavior of methanol and formate in a series of tough phenyl acrylate-based cross-linked IEMs. We then investigate the effects of a structural modification on mixed solute transport behavior by introducing quaternary carbons within the membrane. We measured the relative permittivity properties of swollen films to determine if the water hydrogen bonding environment within the IEMs, which is related to maintaining selective ion transport within the membrane (electrolytes over CO2 reduction products), was impacted by various organic solutes. We observed films with methacrylate backbone linkages have effectively constant relative permittivities when exposed to solutions containing methanol, formate, and a mix thereof. These findings may assist in designing membranes for applications, including CO2 reduction cells and water–organic separation.

Gene expression profiles in Malpighian tubules of the vector leafhopper Psammotettix striatus (L.) revealed regional functional diversity and heterogeneity

BackgroundMany leafhoppers are known as pests and disease vectors of economically important plants. Previous studies of the physiological functions of vector leafhoppers have mainly focused on the salivary glands and the alimentary tract that are deemed to be associated with digestion, host defense and phytoplasma and/or virus transmission. By contrast, the significance of Malpighian tubules (MTs) is less studied. To clarify the physiological function of MTs of the vector leafhopper Psammotettix striatus that transmits phytoplasma triggering the wheat blue dwarf disease, we performed a transcriptome study on P. striatus MTs and compared gene expression profiles among different anatomical regions in the tubules (i.e., MT1+2, the anterior segment together with the sub-anterior segment; MT3, the inflated segment; and MT4, the distal segment).ResultsTranscriptome of P. striatus MTs generate a total of 42,815 high-quality unigenes, among which highly expressed unigenes are mainly involved in organic solute transport, detoxification and immunity in addition to osmoregulation. Region-specific comparative analyses reveal that all these MT regions have functions in osmoregulation, organic solute transport and detoxification, but each region targets different substrates. Differential expression and regional enrichment of immunity-related effector activities and molecules involved in phagocytosis and the biosynthesis of antimicrobial peptides among different regions indicate that MT1+2 and MT4 have the ability to eliminate the invading pathogens. However, in MT3 which secrets brochosomes to the integument and eggs as physical barriers, disulfide-isomerase, acidic ribosomal protein P and many other unigenes were highly expressed, which can be attractive candidate genes for future studies of the biosynthesis and the origin of brochosomes.ConclusionsPsammotettix striatus MTs perform multiple physiological functions as versatile organs than just excretory organs with osmoregulatory function. Heterogeneity of physiological functions among different MT regions is related to organic solute transport, detoxification, immunity and brochosome biosynthesis in addition to osmoregulation, and each region targets different substrates. These functions may be helpful for P. striatus to resist pathogens from habitats and to utilize a wider range of host plants, which may assist the transmission and spread of phytoplasmas. The results provide potential molecular targets for the exploit of chemical and/or gene-silencing insecticides.

Solute Transport Controls Membrane Tension and Organellar Volume.

The regulation of cellular volume in response to osmotic change has largely been studied at the whole cell level. Such regulation occurs by the inhibition or activation of ionic and organic solute transport pathways at the cell surface and is coincident with remodelling of the plasma membrane. However, it is only in rare instances that osmotic insults are experienced by cells and tissues. By contrast, the relatively minute luminal volumes of membrane-bound organelles are constantly subject to shifts in their solute concentrations as exemplified in the endocytic pathway where these evolve alongside with maturation. In this review, we summarize recent evidence that suggests trafficking events are in fact orchestrated by the solute fluxes of organelles that briefly impose osmotic gradients. We first describe how hydrostatic pressure and the resultant tension on endomembranes can be readily dissipated by controlled solute efflux since water is obliged to exit. In such cases, the relief of tension on the limiting membrane of the organelle can promote its remodelling by coat proteins, ESCRT machinery, and motors. Second, and reciprocally, we propose that osmotic gradients between organellar lumens and the cytosol may persist or be created. Such gradients impose osmotic pressure and tension on the endomembrane that prevent its remodelling. The control of endomembrane tension is dysregulated in lysosomal storage disorders and can be usurped by pathogens in endolysosomes. Since trafficking and signaling pathways conceivably sense and respond to endomembrane tension, we anticipate that understanding how cells control organellar volumes and the movement of endocytic fluid in particular will be an exciting new area of research.

Transport of organic solutes in ion-exchange membranes: Mechanisms and influence of solvent ionic composition

Ion-exchange membrane (IEM)-based processes are used in the industry or in the drinking water production to achieve selective separation. The transport mechanisms of organic solutes/micropollutants (i.e., paracetamol, clofibric acid, and atenolol) at a single-membrane level in diffusion cells were similar to that of salts (i.e., diffusion, convection, and electromigration). The presence of an equal concentration of salts at both sides of the membrane slightly decreased the transport of organics due to lower diffusion coefficients of organics in salts and the increase of hindrance and/or decrease of partitioning in the membrane phase. In the presence of a salt gradient, diffusion was the main transport mechanism for non-charged organics, while the counter-transport of salts promoted the transport of charged organics through electromigration (electroneutrality). Conversely, the co-transport of salts hindered the transport of charged organics, where diffusion was the main transport mechanism of the latter. Although convection played a role in the transport of non-charged organics, its influence on the charged solutes was minimal due to the dominant electromigration. Positron annihilation lifetime spectroscopy showed a bimodal size distribution of free-volume elements of IEMs, with both classes of free-volume elements contributing to salt transport, while larger organics can only transport through the larger class.

Lateral Transport of Organic and Inorganic Solutes.

Organic (e.g., sugars and amino acids) and inorganic (e.g., K+, Na+, PO42−, and SO42−) solutes are transported long-distance throughout plants. Lateral movement of these compounds between the xylem and the phloem, and vice versa, has also been reported in several plant species since the 1930s, and is believed to be important in the overall resource allocation. Studies of Arabidopsis thaliana have provided us with a better knowledge of the anatomical framework in which the lateral transport takes place, and have highlighted the role of specialized vascular and perivascular cells as an interface for solute exchanges. Important breakthroughs have also been made, mainly in Arabidopsis, in identifying some of the proteins involved in the cell-to-cell translocation of solutes, most notably a range of plasma membrane transporters that act in different cell types. Finally, in the future, state-of-art imaging techniques should help to better characterize the lateral transport of these compounds on a cellular level. This review brings the lateral transport of sugars and inorganic solutes back into focus and highlights its importance in terms of our overall understanding of plant resource allocation.

Impact of Clinical Use of Parenteral Lipid Emulsions on Bile Acid Metabolism and Composition in Neonatal Piglets.

Neonates with intestinal failure dependent on parenteral nutrition (PN) are at risk of intestinal failure-associated liver disease (IFALD). PN lipid composition relates to the risk of IFALD, but the mechanisms are poorly understood. We investigated the effects of soybean oil (SO), a mixed-lipid (ML) emulsion containing fish oil (FO), and a pure FO. We hypothesized FO-containing PN lipids would result in increased gene expression of canalicular bile acid transporters and a larger, more hydrophilic bile acid pool, predictive of increased bile flow. Neonatal piglets were allocated to receive 1 of SO, ML, or FO throughout 14 days of PN feeding. Relative expression of genes involved in bile acid synthesis and transport were determined through quantitative polymerase chain reaction. Bile secreted from the liver was collected and measured. Bile acid composition was determined using tandem mass spectrometry. Regression analysis was used to determine predictors of bile flow. PN reduced bile acid secretion (P < .001). FO-containing PN lipids were associated with greater expression of bile acid and organic solute transport genes (P < .05) and greater secretion of hydrophobic bile acids (P < .001). Farnesoid X receptor (P = .01), bile salt export pump (P < .01), multidrug resistant protein 2 (P < .01), and unconjugated hyocholic acid (P < .001) independently predicted bile flow. PN lipid modulation altered bile acid metabolism and composition. These alterations may explain the hepatoprotective effects of FO-containing PN lipids and support their use in the prevention and treatment of IFALD.

Evolution and palaeophysiology of the vascular system and other means of long-distance transport.

Photolithotrophic growth on land using atmospheric CO2 inevitably involves H2O vapour loss. Embryophytes greater than or equal to 100 mm tall are homoiohydric and endohydric with mass flow of aqueous solution through the xylem in tracheophytes. Structural details in Rhynie sporophytes enable modelling of the hydraulics of H2O supply to the transpiring surface, and the potential for gas exchange with the Devonian atmosphere. Xylem carrying H2O under tension involves programmed cell death, rigid cell walls and embolism repair; fossils provide little evidence on these functions other than the presence of lignin. The phenylalanine ammonia lyase essential for lignin synthesis came from horizontal gene transfer. Rhynie plants lack endodermes, limiting regulation of the supply of soil nutrients to shoots. The transfer of organic solutes from photosynthetic sites to growing and storage tissues involves mass flow through phloem in extant tracheophytes. Rhynie plants show little evidence of phloem; possible alternatives for transport of organic solutes are discussed. Extant examples of the arbuscular mycorrhizas found in Rhynie plants exchange soil-derived nutrients (especially P) for plant-derived organic matter, involving bidirectional mass flow along the hyphae. The aquatic cyanobacteria and the charalean Palaeonitella at Rhynie also have long-distance (relative to the size of the organism) transport.This article is part of a discussion meeting issue 'The Rhynie cherts: our earliest terrestrial ecosystem revisited'.

Solutes in native plants in the Arabian Gulf region and the role of microorganisms: future research

One of the outstanding challenges facing humankind is increasing crop production under various types of severe environmental conditions. Many measures have been taken to adopt molecular and biotechnological approaches that lead to the development of transgenic plants able to deal with such harsh and polluted environments. However, such solutions could be very expensive and require considerable efforts and time to achieve these objectives. The main objective of this review is to discuss the new biological solutions that have emerged in the last decade, as environmentally friendly approaches, perhaps to support and/or replace the present efforts. These solutions based on plant–microbe interactions could be a lifeline and promising alternative strategy to create plants with a high resistance to the extreme environments. During the last two decades research projects have been conducted to study the ecology, identify the features, and the ecophysiology of native plants and the associated microorganisms in the Arabian Gulf region and particularly in Qatar. Many physiological and biochemical parameters have been determined, including organic solutes (amino acids like proline, glycinebetaine, soluble sugars, etc.), photosynthetic pigments, organic acids and inorganic ions especially heavy metals, along with the physical and chemical properties of the soil in various locations of the State of Qatar. Also, the microorganisms adjacent to and associated with these native plants were identified to elucidate the possible roles in the soil biota in supporting these plants against extreme environmental conditions. Investigations of native plants in the Arabian Gulf states during the last decade have shown that wild plants exhibit different abilities to accumulate organic solutes to cope with the harsh natural environments. Pollution is a major factor stressing wildlife in this region due to the expansion of urban sectors and industrial activities of oil and gas. Compatible osmolytes, like proline, accumulate in wild plants in response to severe environmental conditions and heavy metal contaminated soil. Accumulation of these solutes in plant tissues could provide some level of adaptation and resistance against all these types of environmental stresses. We present some promising efforts in the Arabian Gulf region to remediate desert soil and water polluted with heavy metals and petroleum hydrocarbons. Substantial evidence is introduced about the roles of microorganisms associated with wild plants in natural habitats, such association may help them cope with the extreme stresses. Possible mechanisms adopted by microorganisms in alleviating the harsh abiotic stresses facing the wild life are discussed, one of which is the promotion of biosynthesis and transport of organic solutes to the plants. Also, the main possibilities of the origin of activities of the accumulation of compatible organic solutes are suggested and the objectives of the future research are discussed.

Use of column experiments to investigate the fate of organic micropollutants – a review

Abstract. Although column experiments are frequently used to investigate the transport of organic micropollutants, little guidance is available on what they can be used for, how they should be set up, and how the experiments should be carried out. This review covers the use of column experiments to investigate the fate of organic micropollutants. Alternative setups are discussed together with their respective advantages and limitations. An overview is presented of published column experiments investigating the transport of organic micropollutants, and suggestions are offered on how to improve the comparability of future results from different experiments. The main purpose of column experiments is to investigate the transport and attenuation of a specific compound within a specific sediment or substrate. The transport of (organic) solutes in groundwater is influenced by the chemical and physical properties of the compounds, the solvent (i.e., the groundwater, including all solutes), and the substrate (the aquifer material). By adjusting these boundary conditions a multitude of different processes and related research questions can be investigated using a variety of experimental setups. Apart from the ability to effectively control the individual boundary conditions, the main advantage of column experiments compared to other experimental setups (such as those used in field experiments, or in batch microcosm experiments) is that conservative and reactive solute breakthrough curves can be derived, which represent the sum of the transport processes. There are well-established methods for analyzing these curves. The effects observed in column studies are often a result of dynamic, non-equilibrium processes. Time (or flow velocity) is an important factor, in contrast to batch experiments where all processes are observed until equilibrium is reached in the substrate-solution system. Slight variations in the boundary conditions of different experiments can have a marked influence on the transport and degradation of organic micropollutants. This is of critical importance when comparing general results from different column experiments investigating the transport behavior of a specific organic compound. Such variations unfortunately mean that the results from most column experiments are not transferable to other hydrogeochemical environments but are only valid for the specific experimental setup used. Column experiments are fast, flexible, and easy to manage; their boundary conditions can be controlled and they are cheap compared to extensive field experiments. They can provide good estimates of all relevant transport parameters. However, the obtained results will almost always be limited to the scale of the experiment and are not directly transferrable to field scales as too many parameters are exclusive to the column setup. The challenge for the future is to develop standardized column experiments on organic micropollutants in order to overcome these issues.

Liquid methanol sorption, diffusion and permeation in charged and uncharged polymers

Abstract There are few studies of the impact of membrane charge on ion and organic uncharged solute transport in polymers. This study was aimed at addressing the lack of such fundamental information in the literature. Liquid methanol sorption, diffusion and permeation in water swollen, cross-linked, uncharged poly(ethylene glycol) diacrylate (XLPEGDA) and in charged membranes were investigated. Membrane water content significantly influences methanol solubility, diffusivity and permeability, with more swollen membranes having faster methanol transport rates. The Mackie-Meares model was used to interpret and correlate diffusion data. The Flory-Rehner theory for ternary systems was used to interpret methanol sorption isotherms in XLPEGDA-based polymers. Methanol and sodium chloride transport patterns are similar in neutral hydrogels, while substantial differences are observed in ion exchange polymers. These differences are ascribed to sodium chloride transport in charged polymers being strongly influenced by Donnan exclusion, while methanol sorption and diffusion are not.

A Novel Di-Leucine Motif at the N-Terminus of Human Organic Solute Transporter Beta Is Essential for Protein Association and Membrane Localization.

The heteromeric membrane protein Organic Solute Transporter alpha/beta is the major bile acid efflux transporter in the intestine. Physical association of its alpha and beta subunits is essential for their polarized basolateral membrane localization and function in the transport of bile acids and other organic solutes. We identified a highly conserved acidic dileucine motif (-EL20L21EE) at the extracellular amino-tail of organic solute transporter beta from multiple species. To characterize the role of this protein interacting domain in the association of the human beta and alpha subunits and in membrane localization of the transporter, Leu20 and Leu21 on the amino-tail of human organic solute transporter beta were replaced with alanines by site-directed mutagenesis. Co-immunoprecipitation study in HEK293 cells demonstrated that substitution of the leucine residues with alanines prevented the interaction of the human beta mutant with the alpha subunit. Membrane biotinylation demonstrated that the LL/AA mutant eliminated membrane expression of both subunits. Computational-based modelling of human organic solute transporter beta suggested that the LL/AA mutation substantially alters both the structure and lipophilicity of the surface, thereby not only affecting the interaction with the alpha subunit but also possibly impacting the capacity of the beta subunit to traffick through the cell and interact with the membrane. In summary, our findings indicate that the dileucine motif in the extracellular N-terminal region of human organic solute transporter beta subunit plays a critical role in the association with the alpha subunit and in its polarized plasma membrane localization.

Role of permeate flux and specific membrane-foulant-solute affinity interactions [formula omitted] in transport of trace organic solutes through fouled nanofiltration (NF) membranes

In the literature, sieving effects, charge interactions and adsorptive/hydrophobic interactions have been named as major mechanisms influencing the rejection of trace organic compounds (TOrCs). However, dominant mechanisms influencing TOrC rejection by fouled membranes are not yet fully understood. Most studies have attributed the decline in rejection to cake-enhanced concentration polarisation (CECP) effects and have overlooked the influence of flux decline and attractive membrane-TOrC interactions. Therefore, the aim of this study was to investigate the role of various factors in TOrC rejection for nanofiltration (NF) membranes fouled in cross-flow filtration. To further gain insight into the role of affinity interactions on TOrC rejection, membrane-solute interaction energies (∆Gslm) were computed from the contact angle measurements based on the Lifshitz-van der Waals/acid-base approach. A novel fouling approach (termed sequential fouling) is used to investigate CECP effects for different fouling layers. Sequential fouling results are validated using the CECP model. For a virgin membrane, TOrCs are rejected through sieving mechanisms and repulsive non-electrostatic membrane-TOrC interactions. Upon fouling (especially in the presence of calcium), there was an improvement in the rejection of some TOrCs (solute permeation decreased) due to an improvement in sieving effects. The rejection of some TOrCs decreased over time (solute permeation increased) but the rejection values were close to those of the virgin membrane at similar fluxes showing the influence of flux. When solute permeation increased as a result of fouling, TOrC transport was mainly influenced by non-electrostatic membrane-TOrC affinity interactions and CECP effects (as evidenced by novel sequential fouling experiments and the CECP model).

Tumor suppressor gene OSCP1/NOR1 regulates apoptosis, proliferation, differentiation, and ROS generation during eye development of Drosophila melanogaster.

OSCP1/NOR1 (organic solute carrier partner 1/oxidored nitrodomain-containing protein 1) is a known tumor suppressor protein. OSCP1 has been reported to mediate transport of various organic solutes into cells; however, its role during development has not yet been addressed. Here we report the results of studies on dOSCP1 (the Drosophila ortholog of hOSCP1) to elucidate the role of OSCP1/NOR1 during development. Knockdown of dOSCP1 in the eye imaginal discs induced a rough-eye phenotype in adult flies. This phenotype resulted from induction of caspase-dependent apoptosis followed by a compensatory cell proliferation and generation of reactive oxygen species in eye imaginal discs. The induction of apoptosis appears to be associated with down-regulation of the anti-apoptotic Buffy gene and up-regulation of the pro-apoptotic Debcl gene. These effects of knockdown of dOSCP1 lead to mitochondrial fragmentation, degradation, and a shortfall in ATP production. We also found that knockdown of dOSCP1 causes a defect in cone cell and pigment cell differentiation in pupal retinae. Moreover, mutations in epidermal growth factor receptor pathway-related genes, such as Spitz and Drk, enhanced the rough-eye phenotype induced by dOSCP1 knockdown. These results suggest that dOSCP1 positively regulates the epidermal growth factor receptor signaling pathway. Overall, our findings indicate that dOSCP1 plays multiple roles during eye development in Drosophila.

Structural characterization and subcellular localization of Drosophila organic solute carrier partner 1.

BackgroundOrganic solute carrier partner 1 (OSCP1) is known to facilitate the transport of various organic solutes into cells and reported to play a role in cell growth and cell differentiation. Moreover, OSCP1 is known as a tumor suppressor gene that is frequently down-expressed in nasopharyngeal carcinomas and acute myeloid leukemia. However, the underlying mechanisms of action remain unclear and the subcellular localization of OSCP1 has yet to be determined in detail.ResultsDrosophila contains a single orthologue of OSCP1 (dOSCP1) that shares 58% homology with its human counterpart. To study the expression pattern and subcellular localization of dOSCP1, we prepared a specific antibody. Subcellular localization analyses of dOSCP1 with these revealed localization in the plasma membrane, endoplasmic reticulum, Golgi apparatus and mitochondria, but no detection in cytosol. dOSCP1 signals were also detected in the nucleus, although at weaker intensity than in plasma membranes and subcellular organelles. In addition, native polyacrylamide gel electrophoresis analysis with and without β-mercaptoethanol treatment revealed that recombinant dOSCP1 forms dimers and trimers in solution. The dimer form of dOSCP1 could also be detected by Western immunoblot analyses in third instar larval extracts.ConclusionsThe data revealed that dOSCP1 localizes not only in the plasma membrane but also in the nucleus, ER, Golgi apparatus and mitochondria. It is therefore conceivable that this protein may interact with various partners or form multimeric complexes with other proteins to play multiple roles in cells, providing clues to understanding the functions of dOSCP1 during Drosophila development.

Downregulation of Peptide Transporters PEPT1 and PEPT2 by Oxidative Stress Responsive Kinase OSR1

Background/Aims: OSR1 (oxidative-stress-responsive kinase 1) participates in the regulation of renal tubular ion transport, cell volume and blood pressure. Whether OSR1 contributes to the regulation of organic solute transport remained; however, elusive. The present study thus explored the OSR1 sensitivity of the peptide transporters PEPT1 and PEPT2. Methods: cRNA encoding PEPT1 or PEPT2 were injected into Xenopus oocytes without or with additional injection of cRNA encoding wild-type OSR1, WNK1 insensitive inactive ^T185AOSR1, constitutively active ^T185EOSR1, and catalytically inactive ^D164AOSR1. Electrogenic peptide (glycine-glycine) transport was determined by dual electrode voltage clamp, the abundance of hemagglutinin-tagged PEPT2 (PEPT2-HA) by chemiluminescence. Results: In Xenopus oocytes injected with cRNA encoding PEPT1 or PEPT2, but not in oocytes injected with water, the dipeptide gly-gly (2 mM) generated an appreciable inward current (I_gly-gly). Coexpression of OSR1 significantly decreased I_gly-gly in both PEPT1 and PEPT2 expressing oocytes. The effect of OSR1 coexpression on I_gly-gly in PEPT1 expressing oocytes was mimicked by coexpression of ^T185EOSR1, but not of ^D164AOSR1 or ^T185AOSR1. Kinetic analysis revealed that coexpression of OSR1 decreased maximal I_gly-gly. OSR1 further decreased the PEPT2-HA protein abundance in the cell membrane. Conclusion: OSR1 has the capacity to downregulate the peptide transporters PEPT1 and PEPT2 by decreasing the carrier protein abundance in the cell membrane.

Proteomic-Based Insight into Malpighian Tubules of Silkworm Bombyx mori

Malpighian tubules (MTs) are highly specific organs of arthropods (Insecta, Myriapoda and Arachnida) for excretion and osmoregulation. In order to highlight the important genes and pathways involved in multi-functions of MTs, we performed a systematic proteomic analysis of silkworm MTs in the present work. Totally, 1,367 proteins were identified by one-dimensional gel electrophoresis coupled with liquid chromatography-tandem mass spectrometry, and as well as by Trans Proteomic Pipeline (TPP) and Absolute protein expression (APEX) analyses. Forty-one proteins were further identified by two-dimensional gel electrophoresis. Some proteins were revealed to be significantly associated with various metabolic processes, organic solute transport, detoxification and innate immunity. Our results might lay a good foundation for future functional studies of MTs in silkworm and other lepidoptera.

Effect of molecular packing density and intermolecular interactions on solute transport in supported liquid crystalline membranes

The transport of organic solutes in 4-(trans-4′-4′-n-pentylcyclohexy)-benzonitrile (PCH5) and 4-cyano-4′-octylbiphenyl (8CB) supported liquid crystal (LC) membranes was reported in order to broaden the understanding of mechanisms for solute transport in ordered mesophases. PCH5 was chosen as it exhibits a lower packing density than 8CB but retains a similar molecular structure. Higher sorption and diffusion coefficients were measured in PCH5 compared to 8CB, due primarily to the lower packing density in the PCH5 nematic phase. Solutes capable of forming a single hydrogen bonding with LC molecules exhibited faster diffusion than those with no hydrogen-bonding ability or those capable of multiple hydrogen-bonding interactions. Measurements of relative solubility of pyridine and salicylic acid in 8CB, PCH5 and kerosene confirmed that intermolecular hydrogen bonding plays a stronger role than π−π interactions in solute absorption. Finally, in the absence of differences in hydrogen bonding, higher dipole–dipole interactions resulted in lower diffusivities in LCs.

Cohesion of epithelial ion homeostasis: implementing calcium transport with sodium transporters?

THE ABILITY TO MOVE SOLUTES between the exterior and interior of an organism, between different extracellular compartments, between intracellular and extracellular space, and between organelles and cytoplasm involves a myriad of transport mechanisms; all of which are indispensible for life. Considering the wide variety of solutes that have to be translocated at each of these levels, the precise transport machineries devoted to each solute, and the host of regulatory mechanisms accompanying each of these ensembles, one ponders whether we have enough genes in our genome to achieve these homeostatic feats. The intuitive answer is of course “yes” since we have already succeeded in doing so. While the utilization of multiple proteins to serve the same means bestows redundancy and insurance, the evolution of one protein to execute multiple functions maximizes genetic economy. The fact that one gene product can serve multiple and diverse functions may be a well-known and foregone conclusion to all but is still a remarkable phenomenon to be marveled. Take as an example the most abundant protein in our circulation: hemoglobin. In addition to its known function of carrying O2, hemoglobin also regulates O2 offloading as a metabolic sensor of tissue oxygenation, couples CO2 and nitric oxide transport at the lung and periphery, buffers H, releases vasodilators to directly regulate local blood flow, regulates circadian rhythm of antioxidant, and may even participates in immune surveillance. It is unlikely that this multitasking coevolved completely contemporaneously but was more likely to have done so in tandem, or more likely in “overlapping tandems,” where the needs of one function modulate the evolution of the others. Inherent in this system of serving many masters exist inevitable conflicts that at some point mandate some degree of compromise.