Particulate Membrane Research Articles

Preparation of PLLA membranes with different morphologies for culture of MG-63 Cells

In this work, poly l-lactide (PLLA) membranes with different morphologies were prepared and the equilibrium phase diagram of membrane formation system of ethanol, methylene chloride, and PLLA was studied. Based on the phase diagram, particulate and porous membranes, dominated by crystallization and liquid–liquid demixing, respectively, could be prepared by changing the PLLA concentration of casting solution. In addition, in vitro interaction of MG-63 osteosarcoma cells and PLLA membranes with dense, porous and particulate morphologies was investigated. It was found that the particulate membrane not only could improve cell adhesion and growth, but also could upregulate the osteoblastic phenotype. Therefore, the PLLA membrane with particulate morphology satisfies the biomaterial requirement necessary for temporary scaffold to transplanted osteoblasts and provides a means for the architectural design of more complex tissue-engineered systems.

Myosin II is present in gastric parietal cells and required for lamellipodial dynamics associated with cell activation.

Nonmuscle myosin II has been shown to participate in organizing the actin cytoskeleton in polarized epithelial cells. Vectorial acid secretion in cultured parietal cells involves translocation of proton pumps from cytoplasmic vesicular membranes to the apical plasma membrane vacuole with coordinated lamellipodial dynamics at the basolateral membrane. Here we identify nonmuscle myosin II in rabbit gastric parietal cells. Western blots with isoform-specific antibodies indicate that myosin IIA is present in both cytosolic and particulate membrane fractions whereas the IIB isoform is associated only with particulate fractions. Immunofluorescent staining demonstrates that myosin IIA is diffusely located throughout the cytoplasm of resting parietal cells. However, after stimulation, myosin IIA is rapidly redistributed to lamellipodial extensions at the cell periphery; virtually all the cytoplasmic myosin IIA joins the newly formed basolateral membrane extensions. 2,3-Butanedione monoximine (BDM), a myosin-ATPase inhibitor, greatly diminishes the lamellipodial dynamics elicited by stimulation and retains the pattern of myosin IIA cytoplasmic staining. However, BDM had no apparent effect on the stimulation associated redistribution of H,K-ATPase from a cytoplasmic membrane compartment to apical membrane vacuoles. The myosin light chain kinase inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-7) also did not alter the stimulation-associated recruitment of H,K-ATPase to apical membrane vacuoles, but unlike BDM it had relatively minor inhibitory effects on lamellipodial dynamics. We conclude that specific disruption of the basolateral actomyosin cytoskeleton has no demonstrable effect on recruitment of H,K-ATPase-rich vesicles into the apical secretory membrane. However, myosin II plays an important role in regulating lamellipodial dynamics and cortical actomyosin associated with parietal cell activation.

T Cell Receptor Can Be Recruited to a Subset of Plasma Membrane Rafts, Independently of Cell Signaling and Attendantly to Raft Clustering

The constitutive/inducible association of the T cell receptor (TCR) with isolated detergent-resistant, lipid raft-derived membranes has been studied in Jurkat T lymphocytes. Membranes resistant to 1% Triton X-100 contained virtually no CD3epsilon, part of the TCR complex, irrespective of cell stimulation. On the other hand, membranes resistant either to a lower Triton X-100 concentration (i.e. 0.2%) or to the less hydrophobic detergent Brij 58 (1%) contained (i) a low CD3epsilon amount (approximate 2.7% of total) in resting cells and (ii) a several times higher amount of the TCR component, after T cell stimulation with either antigen-presenting cells or with phytohemagglutinin. It appeared that CD3/TCR was constitutively associated with and recruited to a raft-derived membrane subset because (i) all three membrane preparations contained a similar amount of the raft marker tyrosine kinase Lck but no detectable amounts of the conventional membrane markers, CD45 phosphatase and transferrin receptor; (ii) a larger amount of particulate membranes were resistant to solubilization with 0.2% Triton X-100 and Brij 58 than to solubilization with 1% Triton X-100; and (iii) higher cholesterol levels were present in membranes resistant to either the lower Triton X-100 concentration or to Brij 58, as compared with those resistant to 1% Triton X-100. The recruitment of CD3 to the raft-derived membrane subset appeared (i) to occur independently of cell signaling events, such as protein-tyrosine phosphorylation and Ca(2+) mobilization/influx, and (ii) to be associated with clustering of plasma membrane rafts induced by multiple cross-linking of either TCR or the raft component, ganglioside GM(1). We suggest that during T cell stimulation a lateral reorganization of rafts into polarized larger domains can determine the recruitment of TCR into these domains, which favors a polarization of the signaling cascade.

Structure formation and characterization of EVAL membranes with cosolvent of isopropanol and water

Microporous poly (ethylene-co-vinyl alcohol) (EVAL) membranes can be prepared by the solution casting method in combination of thermally induced phase separation (TIPS) with solvent evaporation. A cosolvent of isopropanol and water (3:2 w/w) is used to prepare the casting solution. EVAL membranes of different bulk or true densities, porosity, flexibility, crystallinity, and structure can be obtained by adjusting the casting temperature. A pseudo-binary temperature–concentration phase diagram of the EVAL–cosolvent system has been proposed, based on the information obtained from SEM, DSC, and light transmittance studies, to account for the membrane formation mechanism. The dense membranes were obtained when the casting temperature was higher than the upper critical solution temperature (UCST) of the system, but they might contain some nonSEM-observable micropores if the casting temperature was below the glass transition temperature ( T g) of EVAL. The porous and the least crystalline membranes with a honeycomb-like morphology were obtained through liquid–liquid demixing and vitrification at a casting temperature between the UCST and the dynamic crystallization temperature ( T c). Highly porous and crystalline membranes were obtained when they were prepared at temperatures near T c. In this case, the particulate membranes were resulted from solid–liquid demixing mainly via TIPS, and membranes with leafy morphology were created through liquid–liquid demixing and then followed with immediately crystallization.

Preparation and application of microporous TPX membranes

In the present work, poly(4-methyl-1-pentene) (TPX) was used to prepare hydrophobic microporous membranes, and the application of the prepared membranes to pervaporation and osmotic distillation was also investigated. The TPX/cyclohexane solution inclines to undergo solid-liquid demixing and form polymer particles at room temperature. The solid-liquid demixing is strongly related to the crystallization process. During membrane formation, the competition between solid-liquid demixing and polymer precipitation determines if particulate membranes can be prepared. By using suitable coagulant, such as propanol, the solid-liquid demixing process occurs before polymer precipitation, particulate TPX membranes with interconnected pores can thus be successfully fabricated. By adjusting the coagulation environment, the pore size of the porous TPX membrane can be tailored. Experiments were performed to evaluate the performance of the prepared membranes in pervaporation and osmotic distillation. The results indicate that the performance of the microporous TPX membranes prepared in the present work is comparable to the commercial PTFE membranes.

Preparation of ethylene vinylalcohol copolymer membranes suitable for ligand coupling in affinity separation

Hydrophilic microfiltration membranes with functional groups that can be used as coupling sites for ligands are of central interest in affinity separation, especially in view of biomedical applications. In this study, we employed ethylene vinyl alcohol copolymer (EVAL) to prepare macrovoid-free open cellular-type membranes with a high internal surface area and interconnectivity that can chemically be modified in aqueous and organic media. To tailor the required membrane morphology, we investigated the ternary water/DMSO/EVAL system and quaternary systems using a series of n-alcohols ( n=2–12) as non-solvent additives in the casting solution. Addition of solvent (DMSO) to the coagulation bath (water) performed in the ternary system to delay the onset of liquid–liquid demixing, resulted in structures dominated by solid–liquid demixing before macrovoid formation was completely suppressed. The symmetric particulate membranes obtained did not display the necessary mechanical strength. Addition of medium chain alcohols ( n=7–8) in the casting solution yielded macrovoid-free cellular membranes with a significantly higher pore interconnectivity and structural integrity upon drying. A model is proposed to understand the influence of the alcohol chain length and concentration on the membrane morphology.

Synthesis and properties of chitosan‐modified poly(vinyl acetate)

AbstractA redox initiator, cerium ammonium nitrate, was used to initiate the graft copolymerization of vinyl acetate (VAc) onto the chitosan chain in a dispersion polymerization at 60°C. With an addition of 0.5–7.5 g of chitosan based on 50 g of VAc, the monomer conversion was found to be between 70 and 80% after 2 h of reaction. The grafting efficiency increased with the amount of chitosan added; yet, the grafting ratio increased slightly and then decreased. After the reaction, a stable dispersion system was observed and the surface of the latex particles was found to be rich in chitosan. All the experimental results indicated that the chitosan molecules not only took part in the graft copolymerization, but also served as a surfactant, providing the stability of the dispersion particles. If the dispersion aqueous solution was oven‐dried, a particulate membrane was formed. The experimental results indicated that the incorporation of poly(vinyl acetate) to the chitosan chains increased the toughness and decreased the water absorption of the chitosan material. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3057–3063, 2002

Decreased phorbol ester binding in the parahippocampal gyrus from subjects with schizophrenia is not associated with changes in protein kinase C.

Combining in situ radioligand binding with autoradiography, we previously identified a reduction of [(3)H]phorbol 12,13-dibutyrate binding in the parahippocampal gyrus from schizophrenic subjects. To determine whether these changes were due to decreases in the level of protein kinase C, we measured [(3)H]phorbol 12,13-dibutyrate binding, levels of the protein kinase C isoforms alpha, beta, delta, epsilon, gamma, eta and theta, as well as protein kinase C activity in crude particulate membranes from parahippocampal gyri of 15 schizophrenic and 15 control subjects. There was a significant decrease in the density (mean +/- SEM: 6.56 +/- 0.73 pmol mg(-1) vs 9.68 +/- 1.22 pmol mg(-1); P < 0.05) and affinity (mean K(D) +/- SEM: 4.64 +/- 0.34 nM vs 2.95 +/- 0.35 nM; P < 0.005) of [(3)H]phorbol 12,13-dibutyrate binding in homogenates from schizophrenic subjects. There were no significant changes in levels of the protein kinase C isoforms which are known to bind phorbol esters or in the activity of protein kinase C in membranes from schizophrenic subjects. These results suggest that there are changes in molecules capable of binding [(3)H]phorbol 12,13-dibutyrate, other than protein kinase C, in the parahippocampal gyrus from subjects with schizophrenia.

Preparation of Chitosan-graft-poly(vinyl acetate) Copolymers and Their Adsorption of Copper Ion

Chitosan-graft-poly(vinyl acetate) copolymers were prepared by a graft copolymerization with a redox initiator, cerium ammonium nitrate. Chitosan molecules not only participated in the reaction, but also served as a role of surfactant. As a result, a stable dispersion solution was observed during the reaction. After drying, particulate membranes were formed because of the rigid chitosan chains at particles’ surface. When the membranes were soaked in the water, the hydrophilic chitosan absorbed a great amount of water, but not the hydrophobic poly(vinyl acetate) chains mainly constituted in the core of particles. A two-stage behavior was observed during the adsorption of copper ion in the copolymer membrane. The first stage was governed by both the diffusion and reaction; whereas only diffusion dominated the second stage. The diffusion rate increased with an increase in the amount of chitosan. In order to increase its mechanical strength and acid resistance, the copolymer membrane was cross-linked with a glutaraldehyde. However, the specific adsorption quantity of copper ion decreased as the extent of cross-linking was increased.

Crossflow Microfiltration of Micro-Sized Mineral Suspensions Using Ceramic Membranes

A variety of well characterized particulate solids and ceramic membranes were used to acquire a range of data, over typical operating conditions, for the crossflow micro-filtration of micro-sized mineral suspensions. Sample data highlight the appropriate particle size for a given ceramic membrane, with the ratio of the mean particle size ( dp ) to mean membrane pore size ( dm ) lying between 2 and 10. In this case, the fouling resistance was caused mainly by the blocking of membrane pores and cake deposition on the membrane surface. The influence of various operating conditions including transmembrane pressure, crossflow velocity, suspension concentration and pH on the filtrate flux were related to the dp/dm ratio, and hence the optimum operating parameters for different dp/dm ratios were obtained. Based on these results, a method for the selection of membrane pore size and process parameters for crossflow microfiltration of micro-sized mineral suspensions using ceramic membranes was determined.

Effect of evaporation temperature on the formation of particulate membranes from crystalline polymers by dry-cast process

The membrane formation of crystalline poly(ethylene-co-vinyl alcohol) (EVAL), poly(vinylidene fluoride) (PVDF), and polyamide (Nylon-66) membranes prepared by dry-cast process was studied. Membrane morphologies from crystalline polymers were found to be strongly dependent on the evaporation temperature. At low temperatures, all the casting solution evaporated into a particulate morphology that was governed by the polymer crystallization mechanism. The rise in the evaporation temperature changed EVAL membrane structure from a particulate to a dense morphology. However, as the temperature increased PVDF and Nylon-66 membranes still exhibited particulate morphologies. The membrane structures obtained were discussed in terms of the characteristics of polymer crystallization in the casting solution theoretically. At elevated temperatures the crystallization was restricted for the EVAL membrane because the increase rate in the polymer concentration was fast relative to the time necessary for growth of nuclei. Nonetheless, the time available for PVDF and Nylon-66 with stronger crystalline properties was large enough to form the crystallization-controlled particulate structure that differed in particle size only. In addition, particles in the PVDF membrane were driven together to disappear the boundary, but those in the Nylon-66 membrane exhibited features of linear grain boundary. The difference in particle morphology was attributed to the Nylon-66 with the most strongly crystalline property. Therefore, the kinetic difference in the crystallization rate of the polymer solution play an important role in dominating the membrane structure by dry-cast process.

Investigation of the drug distribution and release characteristics from particulate membranes

A new type of membrane structure has been developed for drug delivery that offers a biphasic release behavior. A mixture of DMSO, poly(ethylene-vinyl alcohol) (EVAL) and drug was precipitated from 1-octanol to form membranes by constituent particles bonded to each other. The drug can be distributed between particles or trapped in the particles during membrane formation, thereby allowing control of release kinetics. The drug release profile from the EVAL membrane was investigated using water as a release medium. Doxorubicin was used as a model drug because a hydrophilic drug can release in water but is only slightly dissolved in 1-octanol during membrane formation. It was found doxorubicin from the EVAL membrane showed a two-step release behavior. The drug release in the first step was rapid. This is probably due to the membrane is macroscopically porous that drug distributing outside the particles diffuses out rapidly. On the contrary, the drug release in the second step was slow and prolonged. This is probably due to drug entrapped in the particle during membrane formation. However, the particle structure is microscopically dense enough to increase the diffusion resistance, thus delaying and lowering the drug release rate. Therefore, such a membrane could be useful for sustained release of hydrophilic drugs. In addition, a mathematical mass transfer model for a two-step release of doxorubicin from the particulate membrane was developed and applied to the analysis of the drug release data. It can be found that the spherical particles encapsulated more than 55% of the doxorubicin and had a very small mass transfer coefficient. These findings suggest that a drug delivery system using a particulate membrane is a promising method but the technique for loading drug in the particle requires further modification.

Effect of the ethylene content of poly(ethylene‐co‐vinyl alcohol) on the formation of microporous membranes via thermally induced phase separation

AbstractPorous poly(ethylene‐co‐vinyl alcohol) (EVOH) membranes were prepared via thermally induced phase separation. The effect of the EVOH ethylene content on the membrane morphology and solute rejection property was investigated. For EVOHs with ethylene contents of 27–44 mol %, polymer crystallization (solid–liquid phase separation) occurred, and the membrane morphology was the particulate structure. However, the liquid–liquid phase separation occurred before crystallization for EVOH with a 60 mol % ethylene content. Cellular pores were formed in this membrane. For the particulate membranes, higher solute rejection and lower water permeance were obtained for EVOH with a lower ethylene content. The membrane formed by the liquid–liquid phase separation showed a sharper solute rejection change with a change in the solute radius than the particulate membranes did. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 2583–2589, 2001

Glycoprotein synthesis at the synapse: fractionation of polypeptides synthesized within isolated dendritic fragments by concanavalin A affinity chromatography

The synthesis of glycosylated proteins at postsynaptic sites was evaluated by combining metabolic labeling of isolated pinched-off dendritic fragments (synaptodendrosomes) with glycoprotein isolation by Con A affinity chromatography. Three major labeled proteins were detected (apparent molecular weights of 128, 42 and 19 kDa) along with seven minor polypeptides. Treatment of the glycoprotein fraction with N-glycosidase F led to shift in the apparent molecular weight of the bands. Also, label incorporation into glycoprotein species was blocked by tunicamycin. Thus, the three prominent polypeptides and most of the minor components of this fraction corresponded to bona fide N-glycoproteins. Incubation of synaptodendrosomes with cycloheximide also inhibited label incorporation into the isolated glycoproteins, indicating that the labeling resulted from local de novo synthesis. Subcellular fractionation revealed that the labeled glycoproteins were present in soluble and particulate fractions, mainly microsomes and synaptic membranes, and one of the species (42 kDa) appeared in the incubation medium, indicating secretion. In addition, these glycoproteins were dissimilarly distributed in several brain regions, and were expressed differentially during development, reaching their highest level of synthesis during the period of synaptogenesis. These results provide evidence for local dendritic synthesis of particular glycoprotein components of the synapse.

Preparation of EVAL membranes with smooth and particulate morphologies for neuronal culture

In this work, the in vitro interaction of cerebellar granule neurons prepared from 7-day-old Wistar rats and poly ethylene-co-vinyl alcohol (EVAL) membranes was investigated. Cells were cultured in smooth and particulate EVAL membranes for up to 7 days. Particulate membranes were prepared by using 1-octanol to precipitate EVAL solutions in DMSO. Such a membrane was microporous characterized by a packed bed of particles. Voids left between the aggregated particles formed a continuous and interconnected porous network. Crystallization of the EVAL polymer induced by 1-octanol is responsible for the formation of particulate morphology. The membrane structure and its relationship with cells were examined by scanning electron microscopy and the MTT assay. It was observed that the particulate membrane was more favorable for the neuron culture than the smooth membrane. Neurons seeded on the particulate membrane were able to regenerate with formation of an extensive neuritic network. Therefore, the particulate structure may spatially mediate cellular response that can promote neuronal cell attachment, differentiation and neuritic growth, indicating that the particulate structure should be useful as a new polymer scaffold for nerve repair.

The Rho/Rho-kinase and the phosphatidylinositol 3-kinase pathways are essential for spontaneous locomotion of Walker 256 carcinosarcoma cells.

Signal transduction pathways controlling spontaneous locomotion of Walker carcinosarcoma cells are not well understood. We have therefore investigated the role of signalling proteins in development of polarity and locomotion of these cells. Treatment of the cells with 100 ng/ml pertussis toxin had no significant effect on the percentage of polarized cells. In contrast, 2 different phosphatidylinositol 3-kinase inhibitors (wortmannin and LY-294002) markedly reduced the proportion of polarized cells. Spontaneous locomotion of the cells was also significantly inhibited by these two inhibitors. In agreement with these data, we observed localization of the p85alpha subunit of phosphatidylinositol 3-kinase predominantly in the membrane fraction of Walker carcinosarcoma cells, indicating constitutive activation of this enzyme. We also investigated a role of Rho family proteins. Spontaneous development of polarity was almost completely suppressed by electroporation of the cells in the presence of 4 microg/ml C(3) exoenzyme, which specifically ADP-ribosylates and inactivates Rho. Two downstream targets of Rho, the Rho-activated kinases I and II, were also detected predominantly in the particulate membrane fraction, suggesting constitutive activation. A specific Rho-kinase inhibitor (Y-27632) blocked spontaneous polarization and migration in a concentration-dependent manner. Our results indicate that constitutive activation of the Rho/Rho-kinase pathway and of phosphatidylinositol 3-kinase plays an essential part in spontaneous development of polarity and cell locomotion of these cells.

Galactosyl- and fucosyltransferases in etiolated pea epicotyls: product identification and sub-cellular localisation

Summary Particulate membrane preparations from etiolated pea epicotyls were found to contain fucosyltransferases, which transferred fucose from GDP-fucose onto xyloglucan and N-linked glycoprotein, and galactosyltransferases, which transferred galactose from UDP-galactose onto galactan, xyloglucan, and N-linked glycoprotein. The products were characterised by specific enzyme degradation and by acid and alkaline hydrolysis. All the enzymes were found to be concentrated in the Golgi apparatus. The Golgi apparatus was further fractionated into membranes of low, medium and high-density. The glycoprotein fucosyltransferase activity was present in highest amounts in the medium-density Golgi membranes, while the majority of the xyloglucan fucosyltransferase was present in the low-density Golgi membranes. The majority of the galactan galactosyltransferase (galactan synthase) was found in the low-density membranes, while the glycoprotein galactosyltransferase was equally distributed in all three subfractions.

Serotonin 2A receptors are reduced in the planum temporale from subjects with schizophrenia

[ 3H]ketanserin binding to 5HT 2A receptors was measured in the left planum temporale (sensory speech cortex) from schizophrenic and non-schizophrenic (control) subjects using both particulate membranes and tissue sections. There was a significant decrease in the affinity of [ 3H]ketanserin binding to particulate membranes from schizophrenic subjects who were treated with phenothiazines up to death. Adding 2 nM chlorpromazine to brain tissue from control subjects caused a similar decrease in the affinity of [ 3H]ketanserin binding to particulate membranes. This suggests that the decrease in affinity observed in the phenothiazine-treated subjects was due to residual drugs. In addition, there was a significant decrease in the density of [ 3H]ketanserin binding in both particulate membranes and tissue sections from schizophrenic subjects which did not appear to be due to residual antipsychotic drugs. Analysis of the laminar distribution of 5HT 2A receptors showed that this decrease was greatest in cortical layer III. The decrease in the density of 5HT 2A receptors was significant whether schizophrenic subjects were receiving phenothiazines or haloperidol at the time of death, and there was no correlation between the last recorded dose of antipsychotic drug and 5HT 2A receptor density. These data suggest that a decrease in the density of 5HT 2A receptors in the planum temporale may be associated with the pathology of schizophrenia.

Purification of the acyl-CoA elongase complex from developing rapeseed and characterization of the 3-ketoacyl-CoA synthase and the 3-hydroxyacyl-CoA dehydratase.

Oleoyl-CoA elongase catalyzes four successive reactions: condensation of malonyl-CoA to oleoyl-CoA, reduction, dehydration, and another reduction. Evidence supporting this mechanism and the multienzymatic nature of the elongation complex are reported. A particulate membrane fraction from rapeseed is able to elongate intermediates (R,S) 3-hydroxy-20:0-CoA and (E) 2,3-20:1-CoA to very long chain fatty acids in the presence of malonyl-CoA. Studies of the 3-ketoacyl-CoA synthase activities showed that maximal activity could be measured by using 15 to 30 microM 18:1-CoA and 30 microM malonyl-CoA, and that 18:0-CoA and 18:1-CoA were the best substrates. Comparison of the condensation and the overall elongation activities indicated that condensation is the rate-limiting step of the elongation process. The 3-hydroxyacyl-CoA dehydratase activity was maximal in the presence of 75 microM Triton X-100 and 25 microg of proteins. Finally, the acyl-CoA elongase complex was solubilized and purified. During the purification process, the 3-hydroxyacyl-CoA dehydratase copurified with the elongase complex, strongly suggesting that this enzyme belongs to the elongase complex. The apparent molecular mass of 700 kDa determined for the elongase complex, and the fact that four different polypeptide bands were detected after sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the purified fraction, further suggest that the acyl-CoA elongase is a multienzymatic complex.

Sugar-nucleotide-binding and autoglycosylating polypeptide(s) from nasturtium fruit: biochemical capacities and potential functions

Polypeptide assemblies cross-linked by S-S bonds (molecular mass &amp;gt; 200 kDa) and single polypeptides folded with internal S-S cross-links (&amp;lt; 41 kDa) have been detected by SDS/PAGE in particulate membranes and soluble extracts of developing cotyledons of nasturtium (Tropaeolum majus L.). When first prepared from fruit homogenates, these polypeptides were found to bind reversibly to UDP-Gal (labelled with [14C]Gal or [3H]uridine), and to co-precipitate specifically with added xyloglucan from solutions made with 67% ethanol. Initially, the bound UDP-[14C]Gal could be replaced (bumped) by adding excess UDP, or exchanged (chased) with UDP-Gal, -Glc, -Man or -Xyl. However, this capacity for turnover was lost during incubation in reaction media, or during SDS/PAGE under reducing conditions, even as the glycone moiety was conserved by autoglycosylation to form a stable 41 kDa polypeptide. Polyclonal antibodies raised to a similar product purified from Arabidopsis bound to all the labelled nasturtium polypeptides in immunoblotting tests. The antibodies also inhibited the binding of nasturtium polypeptides to UDP-Gal, the uptake of UDP-[14C]Gal into intact nasturtium membrane vesicles and the incorporation of [14C]Gal into nascent xyloglucan within these vesicles. This is the first direct evidence that these polypeptides facilitate the channelling of UDP-activated sugars from the cytoplasm through Golgi vesicle membranes to lumenal sites, where they can be used as substrates for glycosyltransferases to synthesize products such as xyloglucan.