Immobilized-biomembrane affinity chromatography for binding studies of membrane proteins

Highly stabilized, polymer-lipid membranes prepared on silica microparticles as stationary phases for capillary chromatography

The ability to rapidly screen complex libraries of pharmacological modulators is paramount to modern drug discovery efforts. This task is particularly challenging for agents that interact with lipid bilayers or membrane proteins due to the limited chemical, physical, and temporal stability of conventional lipid-based chromatographic stationary phases. Here, we describe the preparation and characterization of a novel stationary phase material composed of highly stable, polymeric-phospholipid bilayers self-assembled onto silica microparticles. Polymer-lipid membranes were prepared by photochemical or redox initiated polymerization of 1,2-bis[10-(2',4'-hexadieoyloxy)decanoyl]-sn-glycero-2-phosphocholine (bis-SorbPC), a synthetic, polymerizable lipid. The resulting polymerized bis-SorbPC (poly(bis-SorbPC)) stationary phases exhibited enhanced stability compared to particles coated with 1,2-dioleoyl-sn-glycero-phosphocholine (unpolymerized) phospholipid bilayers when exposed to chemical (50 mM triton X-100 or 50% acetonitrile) and physical (15 min sonication) insults after 30 days of storage. Further, poly(bis-SorbPC)-coated particles survived slurry packing into fused silica capillaries, compared to unpolymerized lipid membranes, where the lipid bilayer was destroyed during packing. Frontal chromatographic analyses of the lipophilic small molecules acetylsalicylic acid, benzoic acid, and salicylic acid showed >44% increase in retention times (P<0.0001) for all analytes on poly(bis-SorbPC)-functionalized stationary phase compared to bare silica microspheres, suggesting a lipophilic retention mechanism. Phospholipid membrane-functionalized stationary phases that withstand the chemical and physical rigors of capillary LC conditions can substantially increase the efficacy of lipid membrane affinity chromatography, and represents a key advance toward the development of robust membrane protein-functionalized chromatographic stationary phases.

Methods to immobilize GPCR on the surface of SPR sensors

The G protein-coupled receptors (GPCRs) form one of the largest membrane receptor families. The nature of the ligands that interact with these receptors is highly diverse; they include light, peptides and hormones, neurotransmitters, and small molecular weight compounds. The GPCRs are involved in a wide variety of physiological processes and thus hold considerable therapeutic potential.GPCR function is usually determined in cell-based assays, whose complexity nonetheless limits their use. The use of alternative, cell-free assays is hampered by the difficulties in purifying these seven-transmembrane domain receptors without altering their functional properties. Several methods have been proposed to immobilize GPCR on biosensor surfaces which use antibodies or avidin-/biotin-based capture procedures, alone or with reconstitution of the GPCR physiological microenvironment. Here we propose a method for GPCR immobilization in their native membrane microenvironment that requires no manipulation of the target receptor and maintains the many conformations GPCR can adopt in the cell membrane.

Multiple protein stationary phases: a review

Cellular membrane affinity chromatography stationary phases have been extensively used to characterize immobilized proteins and provide a direct measurement of multiple binding sites, including orthosteric and allosteric sites. This review will address the utilization of immobilized cellular and tissue fragments to characterize multiple transmembrane proteins co-immobilized onto a stationary phase. This approach will be illustrated by demonstrating that multiple transmembrane proteins were immobilized from cell lines and tissue fragments. In addition, the immobilization of individual compartments/organelles within a cell will be discussed and the changes in the proteins binding/kinetics based on their location.

Stabilized phospholipid membranes in chromatography: toward membrane protein-functionalized stationary phases

Transmembrane protein (TMP)-functionalized materials have resulted in powerful new methods in chemical analysis. Of particular interest is the development of high-throughput, TMP-functionalized stationary phases for affinity chromatography of complex mixtures of analytes. Several natural and synthetic phospholipids and lipid mimics have been used for TMP reconstitution, although the resulting membranes often lack the requisite chemical and temporal stability for long-term use, a problem that is exacerbated in flowing separation systems. Polymerizable lipids with markedly increased membrane stability and TMP functionality have been developed over the past two decades. More recently, these lipids have been incorporated into a range of analytical methods, including separation techniques, and are now poised to have a significant impact on TMP-based separations. Here, we describe current methods for preparing TMP-containing stationary phases and examine the potential utility of polymerizable lipids in TMP affinity chromatography.

Identification of metabolites of propyrisulfuron in rats

The metabolites found in the urine, feces and bile of male and female rats administered with (14)C-labeled herbicide, propyrisulfuron [1-(2-chloro-6-propylimidazo[1,2-b]pyridazin-3-ylsulfonyl)-3- (4,6-dimethoxypyrimidin-2-yl)urea] were identified by high-performance liquid chromatography (HPLC) with the ultraviolet (UV) and radioisotope (RI) detectors, tandem mass spectrometry and nuclear magnetic resonance (NMR). Administered (14)C was excreted into the urine (5.7-29.8%) and feces (64.6-97.4%). Urine and bile samples were concentrated and purified using a solid-phase extraction cartridge, and fecal homogenates were extracted using acetonitrile. Conjugates were hydrolyzed with enzyme or hydrochloric acid solution for identification. The proposed major metabolic reactions of propyrisulfuron are as follows: (1) hydroxylation of the pyrimidine ring, propyl group, and imidazopyridazine ring, (2) O-demethylation, (3) cleavage of the pyrimidine ring, and (4) glucuronic acid and sulfate conjugation. The metabolic patterns found are not different among sulfonylurea herbicides.

Assembly of lipid bilayers on silica and modified silica colloids by reconstitution of dried lipid films

A method is presented for the assembly of lipid bilayers on silica colloids via reconstitution of dried lipid films solvent-cast from chloroform within packed beds of colloids ranging from 100 nm to 10 μm in diameter. Rapid solvent evaporation from the packed bed void volume results in uniform distribution of dried lipid throughout the colloidal bed. Fluorescence measurements indicate that significant, if not quantitative, retention of DOPC or DPPC films cast between sub-bilayer and multilayer quantities occurs when the colloids are redispersed in aqueous solution. Phospholipid bilayers assembled in this manner are shown to effectively passivate the surface of 250 nm colloids to nonspecific adsorption of bovine serum albumin. The method is shown to be capable of preparing supported bilayers on colloid surfaces that do not generally support vesicle fusion such as poly(ethylene glycol) (PEG) modified silica colloids. Bilayers of lipids that have not been reported to self-assemble by vesicle fusion, including gel-phase lipids and single-chain diacetylene amphiphiles, can also be formed by this method. The utility of the solid-core support is demonstrated by the facile assembly of supported lipid bilayers within fused silica capillaries to generate materials that are potentially suitable for the analysis of membrane interactions in a microchannel format.

Strategies for quality control of Chinese medicines

Chinese medicines (CM) have been attracting interest and acceptance in many countries. Quality control is vital for ensuring the safety and efficacy of CM. Usually, CM are used as whole plant and/or combination of several herbs, and multiple constituents are responsible for the therapeutic effects. Therefore, quality control of CM is very difficult. To date, the valid method for quantitatively evaluating the quality of CM is poor. In this article, the strategies for quantification, related to the markers, reference compounds and approaches, in quality control of CM were reviewed and discussed.

Recent analytical approaches in quality control of traditional Chinese medicines--a review

Traditional Chinese medicines (TCMs) are gaining more and more attention all over the world, due to their specific theory and long historical clinical practice. But the uncontrollable quality is a bottleneck for its modernization and globalization. This paper reviewed the recent analytical methods in the quality control of TCMs, including screening strategies of bioactive markers from TCMs through biochromatographic methods, the traditional chromatographic methods, DNA methods, as well as the spectroscopic methods, including FT-IR, NIR and NMR. The comprehensive methods, such as fingerprint and multi-component quantification are emphasized; hyphenated techniques, like HPLC-MS, GC-MS, CE-MS, LC-NMR, chemometric methods, and combination of chemical and biological methods, such as biofingerprint, metabolic fingerprint are now more and more widely used in TCMs. In a few word, the analysis and quality control of TCMs are moving towards an integrative and comprehensive direction, in order to better address the inherent holistic nature of TCMs.

The nanodisc: a novel tool for membrane protein studies

A major challenge in the research on membrane-anchored and integral membrane protein complexes is to obtain these in a functionally active, water-soluble, and monodisperse form. This requires the incorporation of the membrane proteins into a native-like membrane or detergent micelle that mimics the properties of the original biological membrane. However, solubilization in detergents or reconstitution in liposomes or supported monolayers sometimes suffers from loss of activity and problematic analyses due to heterogeneity and aggregation. A developing technology termed nanodiscs exploits discoidal phospholipid bilayers encircled by a stabilizing amphipatic helical membrane scaffold protein to reconstitute membranes with integral proteins. After reconstitution, the membrane nanodisc is soluble, stable, and monodisperse. In the present review, we outline the biological inspiration for nanodiscs as discoidal high-density lipoproteins, the assembly and handling of nanodiscs, and finally their diverse biochemical applications. In our view, major advantages of nanodisc technology for integral membrane proteins is homogeneity, control of oligomerization state, access to both sides of the membrane, and control of lipids in the local membrane environment of the integral protein.

Screening and analyzing the potential bioactive components from Shaofu Zhuyu decoction, using human umbilical vein endothelial cell extraction and high-performance liquid chromatography coupled with mass spectrometry

In this paper, a useful method for screening and analyzing the potential bioactive components in bioassay-guided fraction (SF-11) from Shaofu Zhuyu decoction was developed using human umbilical vein endothelial cell (HUVEC) extraction and high-performance liquid chromatography coupled with Q-TOF/MS spectrometry. In addition, the protective effects on HUVEC damage induced by adrenaline in vitro were also investigated. The results showed that SF-11 significantly inhibited the endothelin (ET) release and reversed the NO secretion of HUVEC (p < 0.05), and promoted the PGI(2) release of HUVEC (p < 0.05). Two effective components, paeoniflorin and typhaneoside, from SF-11 were screened and identified using live cell extract and HPLC coupled with Q-TOF/MS spectrometry. The compounds, paeoniflorin and typhaneoside, showed significantly inhibiting effects on the ET release and reversing of NO secretion of HUVEC (p < 0.05), with similar effects to SF-11, and promoting the PGI(2) release of HUVEC at the concentration of 0.208 and 0.013 micromol/mL, respectively (p < 0.05). These data indicated that the method of live cell extraction coupled with HPLC-MS technology is feasible, rapid and useful for screening and analyzing potential bioactive components from TCMs.

The analysis of Radix Angelicae Sinensis (Danggui)

Radix Angelicae Sinensis, known as Danggui in China, is one of the most popular traditional Chinese medicines (TCMs), which is contained by more than 80 composite formulae. Modern researches indicate that phthalides, organic acids and their esters, polysaccharides are main chemical components related to the bioactivities and pharmacological properties of Danggui. Some of them, such as Z-ligustilide and ferulic acid, are selected as marker compounds to evaluate the quality of Danggui frequently. Because of the diversity of chemical structures and characters of these components, analytical methods of Danggui are various, including GC-MS, HPLC-DAD-MS, TLC, CE-DAD, and so on. Besides that, the development of analytical technology makes the quality control of Danggui more effective and reliable. Quality evaluation is from single or several components' analysis to fingerprinting, or in combination. Furthermore, bioactive components screening of Danggui has also attracted much attention, which will help us evaluate the selected marker components to some extent. In this paper, the literatures about the major phytoconstituents of Danggui, quality control and bioactive components screening methods have been reviewed. Main attention is given to the different methodologies developed to perform chemical analysis, including separation, detection and identification.

Allosteric modifiers of neuronal nicotinic acetylcholine receptors: new methods, new opportunities

Allosteric, non-competitive inhibitors (NCIs) of neuronal nicotinic acetylcholine receptors (nAChRs) have been shown to produce a wide variety of clinically relevant responses. Many of the observed effects are desired as the nAChR is the therapeutic target, while others are undesired consequences due to off-target binding at the nAChR. Thus, the determination of whether or not a lead drug candidate is an NCI should play an important role in drug discovery programs. However, the current experimental techniques used to identify NCIs are challenging, expensive, and time consuming. This review focuses on an alternative approach to the investigation of interactions between test compounds and nAChRs based upon liquid chromatographic stationary phases containing cellular fragments from cell lines expressing nAChRs. The development and validation of these phases as well as their use in drug discovery and pharmacophore modeling are discussed.

Comparison of alpha1-adrenergic receptor cell-membrane stationary phases prepared from expressed cell line and from rabbit hepatocytes

A G-protein-coupled receptor-cell-membrane stationary phase (CMSP) has been prepared by immobilizing cell membranes on the surface of silica, as carrier. The resulting HEK293 alpha1A adrenoceptor cell-membrane stationary phase can be used for rapid on-line chromatographic determination of potential subtype-selective alpha1-adrenoceptor ligand-binding affinities for alpha 1-adrenoceptor subtypes. The objective of the research was to study whether cell lines stably overexpressing subtype receptors could improve the sensitivity and specificity of cell-membrane chromatography (CMC) compared with use of homogenized tissue and cells in primary culture. Effects of mobile-phase ionic strength, sample concentration, and the presence of competitive agents on ligand-receptor interaction in CMSP were also evaluated. We found that cell lines stably overexpressing subtype receptors led to improved sensitivity and specificity in CMC. The technique leads to useful procedures-cell-membrane stationary phases may, for example, facilitate exploration of ligand-receptor interaction and determination of ligand-receptor binding affinity in initial screening and separation of lead compounds or active components in Chinese traditional natural medicine and herbs. This might eventually be an important contribution and an addition to our collection of techniques.

Live cell extraction and HPLC–MS analysis for predicting bioactive components of traditional Chinese medicines

A novel strategy for predicting bioactive components in traditional Chinese medicines (TCM) using live cell extraction and high performance liquid chromatography-diode array detection-mass spectrometry (HPLC-DAD-MS) analysis was proposed. The hypothesis is that when cells are incubated together with the extract of TCM, the potential bioactive components in the TCM should selectively combine with the cells, and the relative concentrations of the cell-combining components in the suspension medium should decrease, while the cell-combining components would be detectable in the extract of denatured cells. The identities of the cell-combining components could be determined by HPLC-DAD-MS analysis. Using the proposed approach, the potential bioactive components of Danggui Buxue decoction, a commonly used TCM for anaemia, and its compositions, Radix Angelica Sinensis and Radix Astragli for endothelial cells, were investigated. Six compounds in the extract of Danggui Buxue decoction were detected as the components selectively combined with endothelial cells, among them two were contributed by Radix Angelica Sinensis, and four by Radix Astragli. The identities of four of the six potential bioactive compounds were elucidated as ononoside, calycosin, 3-butylphthalide and ligustilide by HPLC-DAD-MS analysis. The results indicate that the proposed approach may be applied to predict the bioactive candidates in TCM.

Receptor–ligand binding assays: Technologies and Applications

Receptor-ligand interactions play a crucial role in biological systems and their measurement forms an important part of modern pharmaceutical development. Numerous assay formats are available that can be used to screen and quantify receptor ligands. In this review, we give an overview over both radioactive and non-radioactive assay technologies with emphasis on the latter. While radioreceptor assays are fast, easy to use and reproducible, their major disadvantage is that they are hazardous to human health, produce radioactive waste, require special laboratory conditions and are thus rather expensive on a large scale. This has led to the development of non-radioactive assays based on optical methods like fluorescence polarization, fluorescence resonance energy transfer or surface plasmon resonance. In light of their application in high-throughput screening environments, there has been an emphasis on so called "mix-and-measure" assays that do not require separation of bound from free ligand. The advent of recombinant production of receptors has contributed to the increased availability of specific assays and some aspects of the expression of recombinant receptors will be reviewed. Applications of receptor-ligand binding assays described in this review will relate to screening and the quantification of pharmaceuticals in biological matrices.

Development of immobilized membrane-based affinity columns for use in the online characterization of membrane bound proteins and for targeted affinity isolations

Membranes obtained from cell lines that express or do not express a target membrane bound protein have been immobilized on a silica-based liquid chromatographic support or on the surface of an activated glass capillary. The resulting chromatographic columns have been placed in liquid chromatographic systems and used to characterize the target proteins and to identify small molecules that bind to the target. Membranes containing ligand gated ion channels, G-protein coupled receptors and drug transporters have been prepared and characterized. If a marker ligand has been identified for the target protein, frontal or zonal displacement chromatographic techniques can be used to determine binding affinities (K(d) values) and non-linear chromatography can be used to assess the association (k(on)) and dissociation (k(off)) rate constants and the thermodynamics of the binding process. Membrane-based affinity columns have been created using membranes from a cell line that does not express the target protein (control) and the same cell line that expresses the target protein (experimental) after genomic transfection. The resulting columns can be placed in a parallel chromatography system and the differential retention between the control and experimental columns can be used to identify small molecules and protein that bind to the target protein. These applications will be illustrated using columns created using cellular membranes containing nicotinic acetylcholine receptors and the drug transporter P-glycoprotein.

Hypothesis of potential active components in Angelica sinensis by using biomembrane extraction and high performance liquid chromatography

The screening and analysis of bioactive components in traditional Chinese medicines (TCMs) is very important not only for the quality control of crude drugs but also for elucidating the therapeutic principle. In this study, a method for screening potential active components from TCMs was developed by using biomembrane extraction and high performance liquid chromatography. Based on the methodology, aqueous extract of Angelica sinensis (WEAS) was used, and four compounds were detected by HPLC in the desorption eluate of red cell membrane extraction for WEAS. The compounds were identified as ferulic acid, ligustilide, senkyunolide H and senkyunolide I based on their UV, MS and NMR spectra. Actually, ferulic acid and ligustilide are considered as major active components in Angelica sinensis. Therefore, this method may be applied to predict the potential bioactivities of multiple compounds in TCMs simultaneously.

The elution profile of immobilized liposome chromatography: determination of association and dissociation rate constants

The interaction of lipophilic cations, tetraphenylphosphonium and triphenylphosphonium homologues with liposomes was investigated using immobilized liposome chromatography (ILC). Large unilamellar liposomes with a mean diameter of 100 nm were stably immobilized in chromatographic gel beads by avidin-biotin. The distribution coefficient calculated from (Ve-V0)/Vs (Ve, retention volume; V0, the void volume; Vs, the stationary phase volume) was found to be independent of flow rate, injection amount and gel bed volume, which is consistent with chromatograph theory. The relationship between the bandwidth and solvent flow rate did not follow band-broadening theories reported thus far. We hypothesized that the solvent might be forced to produce large eddies, spirals or turbulent flow due to the presence of liposomes fixed in the gel. Therefore, we developed a new theory for ILC elution: The column is composed of a number of thin disks containing liposomes and solution, and within each disk the solution is well mixed. This theory accounts for our results, and we were able to use it to estimate the rate constants of association and dissociation of the phosphonium to/from liposomes.

On the oligomeric state of the red blood cell glucose transporter GLUT1

We stripped human red blood cell membranes of cytoskeleton proteins at pH 12 without reductant, partially solubilized the obtained vesicles by use of octaethylene glycol n-dodecyl ether and purified the glucose transporter GLUT1 by anion-exchange chromatography followed by sulfhydryl-affinity chromatography, which removed most of the nucleoside transporter (NT) and the lipids. Eighty percent of the sulfhydryl-bound GLUT1 could be eluted with sodium dodecyl sulfate (SDS) indicating that the bound protein was multimeric. Matrix-assisted laser desorption ionization-time of flight-mass spectrometry (MALDI-ToF-MS) of the trypsinized major SDS-PAGE zone of the purified material identified GLUT1 but no other membrane protein. Transmembrane helices 1 and 8 were among the detected fragments. The reconstituted purified GLUT1 showed glucose transport activity, although only approximately 0.05 high-affinity cytochalasin B (CB) binding sites were present per GLUT1 monomer. The vesicles used as starting material for the purification showed 0.4 CB sites per GLUT1 monomer, similar to vesicles prepared in the presence of dithioerythritol. The data are consistent with the coexistence of monomeric GLUT1 with high-affinity CB-binding activity and preferentially solubilized multimeric GLUT1 with no CB-binding activity in the red blood cell membrane vesicles prepared without reductant.

Separation methods that are capable of revealing blood–brain barrier permeability

The objective of this review is to emphasize the application of separation science in evaluating the blood-brain barrier (BBB) permeability to drugs and bioactive agents. Several techniques have been utilized to quantitate the BBB permeability. These methods can be classified into two major categories: in vitro or in vivo. The in vivo methods used include brain homogenization, cerebrospinal fluid (CSF) sampling, voltametry, autoradiography, nuclear magnetic resonance (NMR) spectroscopy, positron emission tomography (PET), intracerebral microdialysis, and brain uptake index (BUI) determination. The in vitro methods include tissue culture and immobilized artificial membrane (IAM) technology. Separation methods have always played an important role as adjunct methods to the methods outlined above for the quantitation of BBB permeability and have been utilized the most with brain homogenization, in situ brain perfusion, CSF sampling, intracerebral microdialysis, in vitro tissue culture and IAM chromatography. However, the literature published to date indicates that the separation method has been used the most in conjunction with intracerebral microdialysis and CSF sampling methods. The major advantages of microdialysis sampling in BBB permeability studies is the possibility of online separation and quantitation as well as the need for only a small sample volume for such an analysis. Separation methods are preferred over non-separation methods in BBB permeability evaluation for two main reasons. First, when the selectivity of a determination method is insufficient, interfering substances must be separated from the analyte of interest prior to determination. Secondly, when large number of analytes is to be detected and quantitated by a single analytical procedure, the mixture must be separated to each individual component prior to determination. Chiral separation in particular can be essential to evaluate the stereo-selective permeation and distribution of agents into the brain. In conclusion, the usefulness of separation methods during BBB permeability evaluation is immense and more application of these methods is foreseen in the future.

Drug affinity to immobilized target bio-polymers by high-performance liquid chromatography and capillary electrophoresis

This review addresses the use of high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) as affinity separation methods to characterise drugs or potential drugs-bio-polymer interactions. Targets for the development of new drugs such as enzymes (IMERs), receptors, and membrane proteins were immobilized on solid supports. After the insertion in the HPLC system, these immobilized bio-polymers were used for the determination of binding constants of specific ligands, substrates and inhibitors of pharmaceutical interest, by frontal analyses and zonal elution methods. The most used bio-polymer immobilization techniques and methods for assessing the amount of active immobilized protein are reported. Examples of increased stability of immobilized enzymes with reduced amount of used protein were shown and the advantages in terms of recovery for reuse, reproducibility and on-line high-throughput screening for potential ligands are evidenced. Dealing with the acquisition of relevant pharmacokinetic data, examples concerning human serum albumin binding studies are reviewed. In particular, papers are reported in which the serum carrier has been studied to monitor the enantioselective binding of chiral drugs and the mutual interaction between co-administered drugs by CE and HPLC. Finally CE, as merging techniques with very promising and interesting application of microscale analysis of drugs' binding parameters to immobilized bio-polymers is examined.

Centrifugal and chromatographic analyses of tryptophan and tyrosine uptake by red blood cells and GLUT1 proteoliposomes with permeability estimates and observations on dihydrocytochalasin B

We analyzed transport into liposomes and proteoliposomes, separated the free and internalized radioactively labeled substrates by size-exclusion chromatography (SEC) and observed a net influx owing to nonfacilitated diffusion across the lipid bilayers during the separation. The permeabilities (10(-9) cm/s) of glucose transporter (GLUT1) proteoliposomes were estimated to be 4.6, 1.0, 1.4 and 2.1 for D-glucose, L-glucose, L-Tyr and L-Trp, respectively; 15, 3.3, 5.1 and 2.1 times higher than the corresponding permeabilities of liposomes. These values indicated that GLUT1 did not transport Tyr or Trp, or transported Tyr, and only Tyr, slowly. This interpretation was supported by further analyses. Dihydrocytochalasin B inhibited the transport of Tyr and, partially, Trp into human red blood cells (centrifugal analyses). It did not inhibit Tyr and Trp influx into GLUT1 proteoliposomes, but partitioned strongly into the bilayers and seemed to make them fragile. The GLUT1 inhibitor cytochalasin B and the GLUT1 substrate 2-deoxy-D-glucose did not inhibit Tyr transport into the cells. Upon immobilized biomembrane affinity chromatography, Trp decreased the cytochalasin B retardation by GLUT1 only at levels far above the physiological Trp concentration. Ethanol (commonly added to aqueous solutions for enhancing a compound's solubility) halved the retardation at 4% (v/v) concentration. Drastic modification of the SEC method is required to allow permeability measurements with nonlabeled and highly permeable substrates.

Improved lectin-mediated immobilization of human red blood cells in superporous agarose beads

A new type of agarose bead, superporous agarose, was used as a gel support for immobilization of human red blood cells (RBCs) mediated by wheat germ lectin. The number of immobilized cells was similar to that obtained with commercial wheat germ lectin-agarose but the cell stability appeared to be superior. This allowed improved frontal affinity chromatographic analyses of cytochalasin B (CB)-binding to the glucose transporter GLUT1 which established a ratio of one CB-binding site per GLUT1 dimer for both plain RBCs or those treated with different poly amino acids. The measured dissociation constants, 70+/-14 nM for CB and 12+/-3 mM for glucose binding to GLUT1, are similar to those reported earlier.