Oscillatory transverse electric field enhances mass transfer and protein capacity in ion-exchange electrochromatography

Ion-exchange electrochromatography with an oscillatory electric field perpendicular to mobile-phase flow driven by pressure (pIEEC) was developed with a column design of rectangle cross-section. The effect of electric field strength on the dynamic binding capacity (DBC) was examined by frontal analysis of bovine serum albumin (BSA) adsorption to the packed beds of DEAE Sepharose FF in Tris-glycine buffer (pH 8.2). It was shown that the DBC at 10% breakthrough (Q(10)) in the pIEEC increased linearly with increasing the electric field strength. For example, with a packed-bed height of 15mm and electric potential gradient of 38V/cm, Q(10) increased four times over that in normal ion-exchange chromatography. So, the transverse electric field has created significant electro-kinetic mass transports (electroosmosis and electrophoresis) that intensified exterior liquid-film and intraparticle mass transfers, leading to the increased protein binding capacity. Due to the increased capacity in the pIEEC, partial resolution of BSA and IgG under an overload condition was realized without any process optimization. The results have revealed that an electric potential gradient of 20V/cm was enough to greatly enhance the DBC in the pIEEC, and when necessary, high electric field strength can be realized with a low applied voltage because the side distance of the column is usually an order of magnitude smaller than its height. The use of low voltage to carry out electrochromatography is a significant advantage of the pIEEC over conventional electrochromatography with axial electric field.

Ion-exchange chromatography of hepatitis B virus surface antigen from a recombinant Chinese hamster ovary cell line

About 10% of the Chinese population are chronic carriers of hepatitis B virus (HBV). Thus, the development of a highly efficient process for the preparation of a vaccine based on a recombinant hepatitis B surface antigen (HBsAg) is very important to the Chinese national immunization program. To this end, the ion exchange chromatography recovery of CHO-HBsAg from a recombinant Chinese hamster ovary cell line was shown to increase from about 55 to 80% by the addition of 1% poly(ethylene glycol) (PEG 10,000) to the mobile phase. Furthermore, based on analysis by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), the intact glycoprotein form of CHO-HBsAg was completely preserved by the addition of PEG. In the absence of PEG the glycoprotein form of CHO-HBsAg was also spread out into the high salt elution fraction. High-performance size-exclusion chromatography with on-line multiangle-laser-light scattering (HPSEC-MALLS) analysis was performed to monitor the status of the CHO-HBsAg aggregate structure assembly, particle size and molecular weight distribution after each purification step, and the results showed further that the presence of PEG facilitated the separation and recovery of intact glycoprotein form of CHO-HBsAg and promoted their assembly to proper virus-like particles, which are both important features and prerequisites of their immunogenicity.

Predictive modeling of protein adsorption along the bed height by taking into account the axial nonuniform liquid dispersion and particle classification in expanded beds

Expanded bed adsorption (EBA) is a special chromatography technique with perfect classification of adsorbent particles in the column, thus the performance of protein adsorption in expanded beds is particular, obviously nonuniform and complex along the column. Detailed description of the complex adsorption kinetics of proteins in expanded bed is essential for better analyzing of adsorptive mechanisms, the design of chromatographic processes and the optimization of operation parameters of EBA processes. In this work, a theoretical model for the prediction of protein adsorption kinetics in expanded beds was developed by taking into account the classified distribution of adsorbent particles along the bed height, the nonuniform behaviors of axial liquid dispersion, the axial variation of local bed voidage as well as the axial changes of target component mass transfer. The model was solved using the implicit finite difference scheme combining with the orthogonal collocation method, and then applied to predict the breakthrough behaviors of bovine serum albumin (BSA) on Streamline DEAE and lysozyme on Streamline SP along the bed height in expanded beds under various conditions. In addition, the experiments of front adsorption of BSA on Streamline DEAE at different axial column positions were carried out to reveal the adsorption kinetics of BSA along the bed height in a 20 mm I.D. expanded bed, and the influences of liquid velocity and feed concentration on the breakthrough behaviors were also analyzed. The breakthrough behaviors predicted by the present model were compared with the experimental data obtained in this work and in the literature published. The agreement between the prediction and the experimental breakthrough curves is satisfied.

[Synthesis and evaluation of high performance gel filtration chromatography packing of KH-s-GFC300]

A novel packing for high performance gel filtration chromatography (GFC) was synthesized and characterized. High porosity silica prepared by base-dissolving method was used as the matrix. gamma-(2,3-Epoxy propoxyl) propyltrimethoxysilane was used as the ligand and covalently bonded onto the silica matrix. After acidic hydrolysis, the epoxy groups were converted to the diol groups. Because a condensation tube filled with water at 70 degrees C was used in the grafting reaction, the resulting methanol could easily be discharged from the reaction system to shift the reaction equilibrium to achieve high ligand density. The hydrolysis condition greatly affects ligand density and column efficiency. The high column efficiency is observed when the ligand density is between 2.6 and 3.5 +/- mol/m2. Several proteins, such as cytochrome C, chymotrypsin, ovalbumin, bovine serum albumin, aldolase, ferritin, insulin, gamma-globulin, phosphorylase, actin, carbonic anhydrase, were used to characterize the separation properties of the resulting high performance GFC column. It was shown that the excluded limit of relative molecular mass for the separation of bio-molecules was 300 000. The recovery yield of bovine serum albumin was 99%.

Capillary high-performance liquid chromatography/electrospray ion trap time-of-flight mass spectrometry using a novel nanoflow gradient generator

A type of high-performance liquid chromatography (HPLC) based on a novel nanoflow gradient generator (Asymptotic-Trace-10-Port-Valve (AT10PV) nanoGR generator) was developed and coupled with an electrospray ion trap time-of-flight mass spectrometer (ESI-IT-TOF MS). Stability of the nanoflow GR HPLC system was tested at flow rates of 20 and 50 nL/min by using a nanoflow meter. Average flow rates in a 2-h run were 51.2 nL/min with RSD 0.7% and 21.0 nL/min with RSD 1.8%. Repeatability of analysis of the nanoHPLC/ESI-IT-TOF MS system was also tested by injecting 1.0 microL of trypsin digested bovine serum albumin (BSA) (100 fmol) into a monolithic silica-ODS column (30 microm i.d., 150 mm in length) through a packed silica-ODS trapping column (particle size 5 microm, 150 microm i.d., 10 mm in length). At a flow rate of 50 nL/min, the result demonstrated a reasonably good repeatability of peak retention times (RSD: 0.32-1.1%) and base-ion peak areas (RSD: 4.4-6.6%).

Chitosan beads as molecularly imprinted polymer matrix for selective separation of proteins

Two kinds of molecularly imprinted polymers were prepared using hemoglobin as the imprinting molecule, acrylamide as the functional monomer, chitosan beads and maleic anhydride-modified chitosan beads as matrixes, respectively. Static adsorbing experimental results showed that an equal class of adsorption was formed in the imprinted polymers and the adsorption equilibrium constant and the maximum adsorption capacity were evaluated. Chromatographic characteristics showed that the column bedded with the hemoglobin imprinted beads could separate hemoglobin and bovine serum albumin effectively from their mixture, which indicates that the imprinted beads have very higher selectivity for hemoglobin than the non-imprinted with the same chemical composition.

Retention behavior of proteins in size-exclusion electrochromatography with a low-voltage electric field perpendicular to the liquid phase streamline

A novel preparative size-exclusion electrochromatography with an oscillatory low-voltage electric field perpendicular to the liquid phase streamline (pSEEC) was proposed with a column design of rectangular cross-section. The column of 12 cm length was packed with Sephadex G-75, and the retention behavior of bovine serum albumin (BSA) and myoglobin (Myo) was extensively investigated under various conditions. The results indicated that the partition coefficient of a charged protein increased significantly on increasing the current strength as well as the difference between its pI and pH. The partition coefficient also increased on decreasing the mobile phase conductivity. For the gel-excluded protein like BSA, the concentration polarization (CP) on the gel surface induced by the protein electromigration was the main reason for the increased retention. For a gel-permeable protein like Myo, both the CP and electrophoretic migration in the solid phase contributed to its increased retention. Further results exhibited that the polarization would be offset by diffusion, because the accumulated protein would flux back to the bulk liquid phase. Therefore, when the electrically induced mass flux was equal to the diffusion flux, the partition coefficient did not change with a further increase of the oscillatory current cycle. Finally, pSEEC was compared with SEC in the separation of protein mixtures of BSA/Myo as well as BSA/Myo/lysozyme. The results showed much better resolutions of the protein mixtures in pSEEC with the column as short as 12 cm. The potential of pSEEC for preparative protein separation was therefore demonstrated.

Selective and sequential adsorption of bovine serum albumin and lysozyme from a binary mixture on nanosized magnetic particles

Magnetic particles about 10 nm in size were prepared by chemical precipitation under nitrogen and used for the selective and sequential adsorption of bovine serum albumin (BSA) (pI = 4.7) and lysozyme (LSZ) (pI = 1.1) under different conditions, such as pH and initial protein concentration. The separation ratio of BSA over LSZ at pH 4.6 is about 5, which is about 1.5 times the separation ratio of LSZ over BSA at pH 11.0. Only 10% of the preadsorbed BSA could be displaced by the sequential adsorption of LSZ at pH 11.0. On the other hand, 60% of the preadsorbed LSZ was desorbed due to the sequential adsorption of BSA at pH 4.6. Over 50% desorption of BSA or LSZ could be achieved either by 0.5 M Na(2)HPO(4) or 0.5 M NaH(2)PO(4) after 2 h. Over 80% of the enzymatic activity of LSZ was preserved when it was desorbed from magnetic particles.

Rapid separation of protein isoforms by capillary zone electrophoresis with new dynamic coatings

Many cellular functions are regulated through protein isoforms. Changes in the expression level or regulatory dysfunctions of isoforms often lead to developmental or pathological disorders. Isoforms are traditionally analyzed using techniques such as gel- or capillary-based isoelectric focusing. However, with proper electro-osmotic flow (EOF) control, isoforms with small pI differences can also be analyzed using capillary zone electrophoresis (CZE). Here we demonstrate the ability to quickly resolve isoforms of three model proteins (bovine serum albumin, transferrin, alpha1-antitrypsin) in capillaries coated with novel dynamic coatings. The coatings allow reproducible EOF modulation in the cathodal direction to a level of 10(-9) m2V(-1)s(-1). They also appear to inhibit protein adsorption to the capillary wall, making the isoform separations highly reproducible both in peak areas and apparent mobility. Isoforms of transferrin and alpha1-antitrypsin have been implicated in several human diseases. By coupling the CZE isoform separation with standard affinity capture assays, it may be possible to develop a cost-effective analytical platform for clinical diagnostics.

[Separation and purification of proteins on monolithic anion-exchange columns]

A monolithic anion-exchange column with glycidyl methacrylate as the functional monomer and ethylene dimethacrylate as the cross linker was prepared by a free radical polymerization. The epoxide groups of the column were modified respectively by triethylamine, diethylamine and ethylenediamine that afforded anionic functionalities required for the anion-exchange chromatographic mode. The properties of the monolithic columns were investigated and the columns were successfully used as stationary phases of high performance liquid chromatography for the separation of proteins. For chromatographic analysis the effects of mobile phase composition and pH on the separation were investigated. The optimum separation for bovine serum albumin, lysozyme and glutathione was achieved with a gradient elution of mobile phase A (0.01 mol/L Tris-HCl (pH 7.0)) and mobile phase B (mobile phase A + 1.0 mol/L NaCl) with a flow rate of 1.0 mL/min at 25 degrees C. The optimum purification for cellulase enzyme was obtained with a gradient elution of mobile phase A (0.01 mol/L Tris-HCl (pH 7.1)) and mobile phase B (mobile phase A + 1.0 mol/L KBr) with the same flow rate and temperature. The columns exhibited good stability, and cellulase enzyme could be separated and purified quickly on the monolithic anion-exchange column modified by diethylamine.

Partition of whey milk proteins in aqueous two-phase systems of polyethylene glycol–phosphate as a starting point to isolate proteins expressed in transgenic milk

Partitioning behaviour of the bovine whey proteins (bovine serum albumin, alpha lactoalbumin and beta lactoglobulin) and alpha-1 antitrypsin in aqueous two-phase systems prepared with polyethyleneglycol (molecular masses: 1000; 1500 and 3350)-potassium phosphate was analysed. Bovine serum albumin and alpha lactoalbumin concentrated in the polyethyleneglycol rich phase with a partition coefficient of 10.0 and 27.0, respectively, while beta lactoglubulin and alpha-1 antitrypsin showed affinity for the phosphate-rich phase with a partition coefficient of 0.07 and 0.01, respectively. An increase of medium pH induced an increase of the partition coefficient of these proteins while the increase in polyethyleneglycol molecular mass induced the opposite behaviour. The system polyethyleneglycol 1500-pH 6.3 showed the best capacity for recovering the alpha-1 antitrypsin with a yield of 80% and a purification factor between 1.5 and 1.8 from an artificial mixture of the milk whey proteins and alpha-1 antitrypsin. The method appears to be suitable as a starting point to isolate proteins expressed in transgenic milk.

Optimization of bovine serum albumin sorption and recovery by hydrogels

Aqueous two-phase systems are composed of aqueous solutions of either two water-soluble polymers, usually polyethylene glycol (PEG) and dextran (Dx), or a polymer and a salt, usually PEG and phosphate or sulfate. Partitioning of proteins in such systems provides a powerful method for separating and purifying mixtures of biomolecules by extraction. If one of the phase forming polymers is a crosslinked gel, then the solution-controlled gel sorption may be considered as a modification of aqueous two-phase extraction. Since PEG/dextran systems are widely used in aqueous two-phase extraction and dextran gels (Sephadex) are common chromatographic media, we choose a PEG/dextran gel system as a model system in this study. The partitioning behavior of pure bovine serum albumin (BSA) in PEG/dextran gel systems is investigated to see the effects of variations in PEG and NaCl concentrations on the partition coefficient K. By making use of the Box-Wilson experimental design, K is shown to be maximized at 9.8 (%, w/w) PEG and 0.2 M NaCl concentrations, respectively, as 182.

Fast, Comprehensive Two-Dimensional HPLC Separation of Tryptic Peptides Based on High-Temperature HPLC

Two-dimensional HPLC (2D-LC) has recently received considerable attention, and is being used as an alternative to 2D gel electrophoresis in proteomics research. The greatest impediment to the widespread use of 2D-LC is the long analysis time ranging up to days per analysis, making the technique impractical for many jobs. Here we focus on improving the speed of gradient separations since these are typically used as the second dimension in peptide separations by 2D-LC. Specifically we describe high-temperature, ultrafast HPLC conditions, along with the instrument modifications needed to reduce the analysis time of each complete second-dimension gradient separation to tens of seconds. Most importantly, this system is capable of generating a high peak capacity (1350) characteristic of comprehensive 2D-LC in a relatively shorter analysis time (20 min) with a sampling rate sufficient to minimize information loss with simpler instrumentation than currently used; this is equivalent to one unit of peak capacity per second.

Improved hollow-fibre membranes for dye-affinity chromatography

Hollow-fibre membranes with different degrees of surface hydrophilicity were obtained by grafting mixtures of glycidyl methacrylate (GMA) and dimethyl acrylamide (DMAA) in various proportions, and Cibacron Blue F3G-A was attached to them through ammonia or glucamine spacers. Membrane hydrophilicity increased with the amount of dimethyl acrylamide in the grafted polymer. As the hydrophilicity increased the permeability decreased from 352 mL/cm2 min MPa for membranes grafted with GMA with ammonia spacer to 12.7 mL/cm2 min MPa for membranes grafted with GMA/DMAA 1/3 with glucamine spacer. Membranes grafted with GMA/DMAA 1/3 with ammonia spacer showed the best performance for BSA and lysozyme adsorption: maximum capacity was 15.3 +/- 2.2 mg BSA/mL membrane and 58.3 +/- 6.6 mg lysozyme/mL membrane while dissociation constants were 0.27 +/- 0.16 and 0.13 +/- 0.12 mg/mL, respectively. Over 80% of adsorbed proteins could be eluted with 2 M NaCl + 20% isopropanol in 20 mM sodium phosphate buffer, pH 7.0.

Capturing sodium dodecyl sulfate-treated protein antigens by antibody affinity electrophoresis

Modifications to antibody affinity electrophoresis for improved detection of proteins have been developed. The bifunctional linker glutaraldehyde is added to the polyacrylamide gel solution for better incorporation of the bait antibody into a distinct region of a 10% w/v polyacrylamide gel. The addition of glutaraldehyde alleviates the need of an electrophoresis buffer with a specific pH. The protein sample to be analyzed is treated with 2% w/v sodium dodecyl sulfate (SDS) to ensure that they carry a negative charge. The negative charge will allow the proteins to migrate towards the cathode and hence pass through the area embedded with the bait antibody. It is observed that electrophoretic migration of bovine serum albumin (BSA) or protein G ceases upon encounter with anti-BSA whereas proteins ovalbumin, beta-lactoglobulin A, and myoglobin migrate freely. However, the addition of 0.1% w/v SDS in the native gel running buffer disrupts the antibody-antigen bond and neither BSA nor protein G can be captured by anti-BSA.

Isoelectric focusing sample injection for capillary electrophoresis of proteins

Carrier ampholyte-free isoelectric focusing (IEF) sample injection (concentration) for capillary electrophoresis (CE) is realized in a single capillary. A short section of porous capillary wall was made near the injection end of a capillary by HF etching. In the etching process, an electric voltage was applied across the etching capillary wall and electric current was monitored. When an electric current through the etching capillary was observed, the capillary wall became porous. The etched part was fixed in a vial, where NaOH solution with a certain concentration was added during the sample injection. The whole capillary was filled with pH 3.0 running buffer. The inlet end vial was filled with protein sample dissolved in the running buffer. An electric voltage was applied across the inlet end vial and etched porous wall. A neutralization reaction occurs at the boundary (interface) of the fronts of H+ and OH-. A pH step or sharp pH gradient exists across the boundary. When positive protein ions electromigrate to the boundary from the sample vial, they are isoelectricelly focused at points corresponding to their pH. After a certain period of concentration, a high voltage is applied across the whole capillary and a conventional CE is followed. An over 100-fold concentration factor has been easily obtained for three model proteins (bovine serum albumin, lysozyme, ribonuclease A). Furthermore, the IEF sample concentration and its dynamics have been visually observed with the whole-column imaging technique. Its merits and remaining problem have been discussed, too.

Fractionation of bovine serum albumin and monoclonal antibody alemtuzumab using carrier phase ultrafiltration

Protein transmission and hence selectivity of separation can be significantly affected by solution pH and ionic strength in protein fractionation using ultrafiltration. Using parameter scanning ultrafiltration, the transmission of bovine serum albumin (BSA) and monoclonal antibody alemtuzumab (Campath-1H) through 300 kDa polyethersulfone (PES) ultrafiltration membranes were studied over a range of pH and salt concentrations, with focus on the likely conditions for achieving "reverse selectivity," i.e., obtaining purified alemtuzumab (approximately 155 kDa) in the permeate. Experimental results demonstrate that the reverse selectivity could be obtained by manipulating the operating conditions such as the solution pH, ionic strength, permeate flux, and system hydrodynamics. With a two-stage batch ultrafiltration process under suitable conditions, the monoclonal antibody alemtuzumab with a purity of > 98% was obtained in the permeate from a feed solution initially containing 0.50 g/l each of BSA and alemtuzumab. Further purity can be expected by selecting more suitable membranes and optimizing operating conditions.

On-line counting of cysteine residues in peptides during electrospray ionization by electrogenerated tags and their application to protein identification

The electrochemically induced mass spectrometric tagging of cysteines by substituted hydroquinones was studied for peptides in a classical electrospray solvent (i.e., MeOH/H2O/AcOH 50/49/1). The tagging efficiency was tested with different hydroquinone compounds on an undecapeptide containing one cysteine residue. 2-carboxymethylhydroquinone was the most reactive probe and revealed to be suitable for cysteine quantification in peptides containing up to three cysteine residues, even in the case of two consecutive cysteines in the sequence. We demonstrate the compatibility of the on-line electrochemical tagging method for the cysteine content analysis of peptides coming from gel-free protein digestion procedures. The identification of bovine serum albumin and human alpha-lactalbumin digest samples in a peptide mapping strategy was greatly improved by the application of the electrotagging technique as post-column treatment. Indeed, the determination of cysteine content in the tryptic peptides provided powerful information in order to enhance the identification score as well as the discrimination against other protein candidates. The tagging method was then applied to the determination of four proteins in a model mixture.

Protein partitioning in aqueous two-phase systems composed of a pH-responsive copolymer and poly(ethylene glycol)

The effect of pH and salt concentration on the partitioning behavior of bovine serum albumin (BSA) and cytochrome c in an aqueous two-phase polymer system containing a novel pH-responsive copolymer that mimics the structure of proteins and poly(ethylene glycol) (PEG) was investigated. The two-phase system has low viscosity. Depending on pH and salt concentration, the cytochrome c was found to preferentially partition into the pH-responsive copolymer-rich (bottom) phase under all conditions of pH and salt concentrations considered in the study. This was caused by the attraction between the positively charged protein and negatively charged copolymer. BSA partitioning showed a more complex behavior and partitioned either to the PEG phase or copolymer phase depending on the pH and ionic strength. Extremely high partitioning levels (partition coefficient of 0.004) and very high separation ratios of the two proteins (up to 48) were recorded in the new systems. This was attributed to strong electrostatic interactions between the proteins and the charged copolymer.

A novel method for simultaneous purification of albumin and immunoglobulin G

A novel method was developed to obtain both highly purified bovine serum albumin (BSA) and immunoglobulin G (IgG), at the same time, on a pilot scale. Heat-isopropyl alcohol was used to denature and precipitate the other plasma proteins, except for BSA and IgG; then, CM-Trisacryl was applied to further purify and isolate BSA and IgG. The new procedure produced highly purified BSA and IgG, 98% and 96.8%, respectively, and yielded ideal output, 2.18% and 0.54%, from starting plasma, respectively. The new technique is a rapid and is an available pilot process to prepare the plasma fractions devoid of cellular components.

Deamidation and cross-linking of gliadin peptides by transglutaminases and the relation to celiac disease

Activation of small intestinal gluten-reactive CD4+ T cells is a critical event in celiac disease. Such cells predominantly recognise gluten peptides in which specific glutamines are deamidated. Deamidation may be catalysed by intestinal tissue transglutaminase (TG2), a protein which is also the main autoantigen in celiac disease. Our aim was to study how the two main catalytic activities of transglutaminase--deamidation and transamidation (cross-linking) of an immunodominant gliadin epitope--are influenced by the presence of acceptor amines in the intestinal mucosa, and thereby contribute to further elucidation of the pathogenetic mechanisms in celiac disease. We prepared monoclonal antibodies, reacting specifically with the non-deamidated epitope QPFPQPQLPYPQPQ-amide and/or the deamidated epitope QPFPQPELPYPQPQ-amide. A solid phase immunoassay combined with gel filtration chromatography was used to analyse deamidation and cross-linking of these peptides to proteins. Our results show that QPFPQPQLPYPQPQ-amide was deamidated when incubated with purified TG2, with fresh mucosal sheets and with mucosal homogenates. Of other transglutaminases tested, only Streptoverticillium transglutaminase was able to generate the deamidated epitope. A fraction of the non-deamidated epitope was cross-linked to proteins, including TG2. The results suggest that intestinal TG2 is responsible for generation of the active deamidated epitope. As the epitope often occurs in a repeat structure, the result may be cross-linking of a deamidated, i.e., activated cell epitope. Alternatively, the deamidation may occur by reversal of the cross-linking reaction. The results provide a basis for the suggestion that binding of a peptide to a protein, in connection to its modification to a T cell epitope, might be a general explanation for the role of TG2 in celiac disease and a possible mechanism for the generation of autoantigens.

Quantitative analysis of membrane fouling by protein mixtures using MALDI-MS

Binary aqueous solutions of bovine serum albumin (BSA) and beta-lactoglobulin (bLG) were subject to flux-stepping and constant flux ultrafiltration to identify the apparent critical flux and to study the mechanisms and factors affecting fouling when the membrane is permeable to one protein component. Membranes from these filtration experiments were analyzed using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) to locate and quantify levels of fouling below and above the apparent critical flux. Hydrophilic (PLTK) regenerated cellulose and hydrophobic (PBTK) polysulfone asymmetric membranes were used, both of 30 kDa nominal molecular weight cut-off. For the hydrophilic PLTK membrane, protein deposition was shown to depend on electrostatic forces, exhibiting little or no fouling when the proteins had the same charge sign as that of the membrane. This was found to apply for both dilute equal mass-per-unit-volume and equimolar binary mixtures. For the PBTK membrane, hydrophobic protein-membrane attractive forces were sufficiently strong to cause deposition of bLG even in the presence of repulsive electrostatic forces. For the PBTK membrane deposition exceeded monolayer coverage below and above apparent critical flux conditions but for the PLTK membrane this generally occurred when the apparent critical flux was exceeded. MALDI-MS was shown to be a facile direct analytical technique for individually quantifying adsorbed proteins on membrane surfaces at levels as low as 50 fmol/mm(2). The high levels of compound specificity inherent to mass spectrometry make this approach especially suited to the quantification of individual components in mixed deposits. In this study, MALDI-MS was found to be successful in identifying and quantifying the protein species responsible for fouling.

Surfactant-aided size exclusion chromatography

The flexibility and selectivity of size exclusion chromatography (SEC) for protein purification can be modified by adding non-ionic micelle-forming surfactants to the mobile phase. The micelles exclude proteins from a liquid phase similar to the exclusion effect of the polymer fibers of the size exclusion resin. This surfactant-aided size exclusion chromatography technology (SASEC) is demonstrated on the separation of two model proteins; bovine serum albumin (BSA) and myoglobin (Myo). The effect of the added surfactants on the distribution behavior of the proteins is predicted adequately by a size exclusion model presented in this paper.

Small-molecule-protein conjugation procedures

Small-molecule-protein conjugates are often required to act as immunogeneic complexes in the production of both monoclonal and polyclonal antibodies against small antigens. When antibodies have been obtained, they (and/or the small antigens) need to be labeled to facilitate their use in diagnostic assays. It is often impossible or extremely expensive to obtain the required conjugates. This chapter therefore discusses the common procedures used to couple small molecules to proteins and the analysis of the resulting conjugates. Practical guidance is given on the coupling of small molecule carboxyl, hydroxyl, and amine residues to amine and sulfhydryl residues on proteins using linkage techniques in which the author has extensive experience. Although a comprehensive list and analysis of every available linker is not given, the practical advice should enable the reader to use any commercially available linker productively to its optimum potential.