Perfusion chromatography

Perfusion chromatography is a technique based on fluid dynamics for reducing stagnant mobile phase mass transfer in liquid chromatography. This is achieved by using supports with large pores that allow mobile phase to flow through particles.

Quantification of antibodies to human growth hormone by high-performance protein G affinity chromatography with fluorescence detection

The technique of high-performance affinity chromatography (HPAC) is applied to the quantitative determination of antibodies to human growth hormone (hGH) in serum from patients. An affinity column consisting of covalently immobilized protein G on a rigid support is used to capture the antibodies. Texas Red labeled hGH (hGH-TR) is used as a fluorescence probe for detecting the anti-hGH antibodies. Calibration curves are established by using a well-characterized monoclonal antibody to hGH (GHC101). The minimum detectable concentration (MDC) of anti-hGH antibody in serum is 250 ng/mL (this represents 10 ng of anti-hGH injected onto the protein G column). Analytical recoveries are 92-110% for seven replicates with 250-4000 ng/mL of GHC101. A precision of 15% relative standard deviation (RSD) can be achieved at the MDC. The precision is better above the detection limit. The linear dynamic range of the method is approximately 2 orders of magnitude. The total fluorescence recovery from the affinity column is greater than or equal to 96%. Sample analysis times are on the order of 20 min. The HPAC technique gives results in absolute units of concentration that correlate well with binding capacity values determined by radioimmunoassay.

Flow-through particles for the high-performance liquid chromatographic separation of biomolecules: perfusion chromatography

This paper reports a new technique for reducing resistance to stagnant mobile phase mass transfer without sacrificing high adsorbent capacity or necessitating extremely high pressure operation. The technique involves the flow of liquid through a porous chromatographic particle, and has thus been termed "perfusion chromatography". This is accomplished with 6000-8000 A pores which transect the particle. Data from electron microscopy, column efficiency, frontal analysis and theoretical modelling all suggest that mobile phase will flow through these large pores. In this manner, solutes enter the interior of the particles through a combination of convective and diffusional transport, with convection dominating for Peclet numbers greater than one. The implications of flow through particles on bandspreading, resolution and dynamic loading capacity are examined. It is shown that the rate of solute transport is strongly coupled to mobile phase velocity such that bandspreading, resolution of proteins and dynamic loading capacity are unaffected by increases in mobile phase velocity up to several thousand centimeters per hour. The surface area of this very large-pore diameter material is enhanced by using a network of smaller, 500-1500 A interconnecting pores between the throughpores. Scanning electron micrographs show that the pore network is continuous and that no point in the matrix is more than 5000-10,000 A from a through-pore. As a consequence, diffusional path lengths are minimized and the large porous particles take on the transport characteristics of much smaller particles but with a fraction of the pressure drop. Capacity and resolution studies show that these materials bind and separate an amount of protein equivalent to that of conventional high-performance liquid chromatography as well as low performance agarose-based media at greater than 10-100 times higher mobile phase velocity with no loss in resolution.

Polyethyleneimine-bonded phases in the separation of proteins by capillary electrophoresis

A hydrophilic, positively charged, durable coating has been developed for capillary electrophoresis of macromolecules. Polyethyleneimine is adsorbed to the inner wall of fused silica capillaries and the adsorbed coating cross-linked into a stable layer. Capillaries of polyethyleneimine-coated silica gave unique separations owing to the reversal of electro-osmotic flow caused by the positively charged coating. The resulting coating was stable from pH 2-12 and could be used over a wide pH range without substantial change in electro-osmotic flow. High-molecular-weight polymers were needed to give thick coatings which mask silanol groups on the wall. Proteins were resolved quickly and efficiently with good recovery using capillaries of 50 cm in length.

Microenvironmental contributions to the chromatographic behavior of subtilisin in hydrophobic-interaction and reversed-phase chromatography

Genetically engineered variants were used to examine how microenvironmental changes in the S1 substrate binding subsite of subtilisin contribute to chromatographic behavior of proteins on hydrophobic-interaction chromatography (HIC) and reversed-phase chromatography (RPC) columns. Gradient elution studies over a wide pH range showed that conditions could be found where a HIC support could separate proteins varying by one amino acid. Although all single-site variants could not be separated by HIC, this chromatographic mode was found to be complementary to cation-exchange chromatography for the separation of such variants. RPC was found to be of much less utility in the resolution of variant proteins. Retention and resolution of subtilisin variants was found to vary on RPC with the concentration and type of mobile phase pairing agent.

Thermodynamic model for electrostatic-interaction chromatography of proteins

A thermodynamic model derived by Record et al. [M. T. Record, Jr., Biopolymers, 14 (1975) 2137 and M. T. Record, Jr., C. F. Anderson and T. M. Lohman, Q. Rev. Biophys., 11 (1978) 103] from Wyman's linkage theory [J. Wyman, Adv. Protein Chem., 19 (1964) 223] using Manning's condensation model [J. Manning, J. Chem. Phys., 51 (1969) 924] was extended to electrostatic interaction chromatography. Mixed, electrostatic and hydrophobic interactions of a model protein, ovalbumin were characterized by ion and water release.

Single amino acid contributions to protein retention in cation-exchange chromatography: resolution of genetically engineered subtilisin variants

Genetically engineered proteins were used to determine the amino acid contributions of surface residues to subtilisin retention in cation-exchange chromatography. Crystallographic data were used to correlate the observed chromatographic behavior with enzymatic structure. Retention times of variants in gradient elution varied by as much as 33% compared to the wild type. The role of both charged and uncharged residues was investigated in isocratic separations and found to significantly influence protein retention in this electrostatically dominant separation method. This study demonstrates the ability of ion-exchange chromatography to discriminate between protein variants differing by a single residue in 275 amino acids.

Dual-column immunoassays using protein G affinity chromatography

Tandem protein G affinity and reversed-phase chromatography (RPC) columns, coupled with a switching valve, were used for on-line immunoassays of antibodies and antigens. Columns with reversibly immobilized antibodies were prepared by adsorbing antibodies on the protein G column. Following antigen capture in the immunoaffinity column, antigen-antibody complexes were desorbed, dissociated, and transferred to the RPC column where they were separated and quantified. This system was used to determine the titer of a rabbit anti-human transferrin antibody sample with a precision of +/- 2%. Quantitation of human transferrin in human serum had a precision of +/- 6% and showed good agreement with rate nephelometry. The linear dynamic range for the transferrin, antigen immunoassay was 5 x 10(1) to 1 x 10(5) ng with a precision of +/- 3.5%.

Reversed-phase liquid chromatography of proteins with strong acids

Small organic acids are generally used as pairing agents at less than 1% concentration in reversed-phase chromatography (RPC) of proteins. When the protein is very hydrophobic and insoluble, as in the case of membrane proteins, up to 60% aq. formic acid has been used. This paper reports a study of the influence of acid concentration on both chromatographic retention and protein structure in RPC. Chromatographic retention increases in proportion to the concentration of organic acid in the mobile phase up to some intermediate concentration. Use of still higher concentrations of acid results in a sharp drop in chromatographic retention with a change in selectivity. The data indicate that the structure of proteins in strong acids are different from that in weak acids. This work examines the reason for this decrease in chromatographic retention at formic and trifluoroacetic acid concentrations above 30% (v/v). Spectroscopic studies show that protein conformation continuously changes with the addition of acid.

Immunological-chromatographic analysis of lysozyme variants

Immunological-chromatographic analysis (ICA) was used to evaluate the cross-reactivities of eight lysozyme variants with five different immobilized monoclonal anti-hen-egg-white lysozyme antibodies. ICA is a dual-column high-performance liquid chromatography-based method in which an immunoaffinity and a conventional analytical column are coupled with a switching valve. Antigens are first captured on the affinity column and then desorbed and concentrated on the second column, where they are separated further. This arrangement permits antigen-antibody interactions occurring on the affinity column to be monitored on-line with the second column. The ICA system was used to perform direct and competitive inhibition binding immunoassays with unlabeled antigens. Seven of the eight lysozymes tested bound to all five immobilized monoclonal antibodies. Competitive inhibition of binding of hen egg white lysozyme to the monoclonal antibody, HyHel-5, was measured by using the variants Japanese quail and bobwhite quail lysozymes as inhibitors. The ratio of the amount of bobwhite quail to Japanese quail lysozyme required to give 50% inhibition of binding of hen egg white determined by ICA compares well with the results obtained by other investigators who used an enzyme-linked immunosorbent assay plate binding assay.

Immobilized-metal affinity and hydroxyapatite chromatography of genetically engineered subtilisin

High-performance immobilized-metal affinity and hydroxyapatite chromatography were employed to investigate the engineered subtilisin S1 binding site microenvironment. Although these methods are classified as affinity techniques, unlike traditional affinity columns, both are capable of probing the entire surface of a molecule. The metal chelate study employed gradient elution to assemble retention maps for a wide range of mobile-phase pH. Resolution of single substitution variants was achieved at the optimum mobile-phase pH. A total of four metals were applied separately to the metal chelate column to investigate ligand specificity with respect to protein retention. Hydroxyapatite chromatography, albeit an established technique, has only recently been developed as a high-performance chromatographic method. Gradient elution separations were performed to determine selectivity. Immobilized-metal affinity chromatography was found to be the more effective method for the separation of site-specific variants.

Immunological-chromatographic analysis

Tandem immunoaffinity and conventional high-performance liquid chromatography columns, coupled with a switching valve, were used for the analysis of single and multicomponent antigen samples. Immunoaffinity columns were prepared by hydrophobic adsorption or covalent immobilization of poly- or monoclonal antibodies on macroporous poly(styrene-divinylbenzene) packing materials. Capacities of these columns were constant through at least 77 cycles. Macromolecular antigens were analyzed at submicrogram levels. Antigens bound to the immunoaffinity column were desorbed and concentrated on a conventional analytical column. Gradient elution on the analytical column separated the desorbed antigen(s) from interfering species and permitted the analysis of all species which bound to the immunoaffinity column. Immunological-chromatographic analysis was useful for purification and discrimination of polypeptides of similar three dimensional structures, such as several lysozyme variants.

Surface-mediated retention effects of subtilisin site-specific variants in cation-exchange chromatography

Wild-type subtilisin and several site-specific variants were resolved on a strong cation-exchange column by isocratic elution and a series of sodium chloride concentrations. Changes in primary sequence at the protein surface have an observable effect on the chromatographic behavior of subtilisin. This supports the concept that three-dimensional structure determines which biopolymer surface residues are in position to interact with the stationary phase surface. The retention data fit the stoichiometric displacement model (SDM) of retention. Plots of ln k' vs. ln 1/[NaCl] yield values for the average number of ionic groups (Z) on the protein that interact with the support matrix. Application of the SDM to the chromatographic retention of the variants has uncovered an unusual phenomenon at the protein surface at low ionic strength. A SDM plot normally provides a linear relationship between ln k' and ln 1/[NaCl] with the slope corresponding to the Z number. This study revealed two lines differing in slope and intercept, indicating that the Z number of subtilisin changes at some intermediate ionic strength of the eluent. These results are attributed to some salt-induced protein surface event that triggers a change in structure. Chromatographic detection of this occurrence reflects the connection between the surface-mediated event and mobile phase ionic strength.

Molecular orientation of immunoglobulin G at high concentration on an ion-exchange sorbent

The change of molecular orientation of IgG, bound on a strong-anion-exchange surface, was studied using a generalization of the stoichiometric displacement model, over the entire range of protein adsorption isotherms. The Z number was found to decrease with increasing stationary phase protein concentration, approaching a limiting value. The analogy of the multiple equilibria model within highly cooperative identical binding sites was suggested as a possible way to evaluate the observed change in Z number with the protein concentration.

Synthesis of a non-porous, polystyrene-based strong anion-exchange packing material and its application to fast high-performance liquid chromatography of proteins

Adsorbed coating technology has been used to produce a strong anion-exchange stationary phase on 3-micron non-porous poly(styrene-divinylbenzene) particles. In order to take full advantage of the excellent kinetic properties of the resultant packing material, small columns of 5 mm X 6 mm I.D. were used. These columns were pressure- and pH-stable and allowed protein separations to be made in less than 1 min at ambient temperature.

Chromatographic resolution of lysozyme variants

There are seven avian lysozyme variants of nearly identical three-dimensional structure which have amino acid substitutions broadly distributed on their surface. By using these protein variants, it was possible to study the relationship between protein structure and chromatographic retention. It was determined that according to the mode of separation various regions of the proteins surface determine chromatographic retention. At one extreme, immunosorbents targeted a very small region on the protein surface. Hydrophobic interaction chromatography was an intermediate case in which one surface domain of the lysozymes controlled chromatographic behavior. At the opposite extreme, cation-exchange columns probed most of the protein surface. It was concluded that identification of random variations in protein structure will be most successfully detected by a separation mode that broadly targets the surface of a protein.

Chromatography of proteins on hydrophobic interaction and ion-exchange chromatographic matrices: mobile phase contributions to selectivity

The effect of mobile phase pH on the retention characteristics of eleven proteins was examined in hydrophobic interaction chromatography (HIC) on a SynChropak propyl stationary phase. Selectivity was shown to change with eluent pH. The effect of the displacing salt on the separation of proteins on a weakly hydrophobic weak-anion-exchange chromatography (AEC) packing was examined. Some differences in selectivity were observed when sodium sulfate was used as the displacing salt, compared to that observed with sodium chloride in the eluent. It was demonstrated that these AEC packings exhibited both electrostatic and hydrophobic properties, depending upon the type and concentration of salt used in the mobile phase. The addition of 20% ethylene glycol to the mobile phase was shown to reduce the hydrophobic interactions. The application of weakly hydrophobic weak-cation-exchange packings to HIC of proteins was demonstrated. Elution of such columns with descending sodium sulfate gradients was found to provide a selectivity different from that observed with a propyl stationary phase. Manipulation of mobile phases was shown to provide useful selectivity as a result of the combination of electrostatic and hydrophobic contributions to the separation process.

Correlation of calcitonin structure with chromatographic retention in high-performance liquid chromatography

Chromatographic selectivity and position specificity were examined by using deletion and substitution analogues of calcitonin (CT), a 32-amino acid polypeptide. The biological activity of CT has been shown to be related to structural features, including a regular spacing of hydrophobic and hydrophilic residues in positions 8-22. The effect of structure on retention behavior in hydrophobic interaction chromatography (HIC) and reversed-phase chromatography (RPC) of 19 CT analogues was examined. No simple correlation was found between chromatographic retention and amino acid composition. Deletion of one leucine residue reduced retention in both chromatographic systems, but the magnitude of the change depended upon the site at which the deletion occurred. For example, deletion analogues des(Leu16)-, des-(Leu12)-, des(Leu10)-, des(Leu9)-, des(Leu4)-, and salmon calcitonin had retention times of 5.22, 8.44, 11.64, 13.53, 15.45, and 20.28 min, respectively, in HIC in contrast to RPC retentions of 15.19, 15.84, 28.53, 27.57, 25.92 and 34.79 min, respectively. Serine deletion was also shown to be position-specific. Non-amphiphilic analogues were eluted before amphiphilic ones. Circular dichroic spectral studies showed that the CT analogues possessed little secondary structure in the HIC solvents in contrast to alpha-helix formation in RPC solvents. The HIC data provided indirect evidence of secondary structure, induced in the amphiphilic CT analogues at the HIC solvent-chromatographic surface interface. Solute-solvent interactions contributed to differences observed between the selectivity of RPC and HIC.

Phase ratio determination in an ion-exchange column having pores partially accessible to proteins

A method is suggested for determination of the hold-up volume and the phase ratio of a protein on a strong anion-exchange chromatographic column, which is based on mercury porosimetry and size-exclusion calibration with polymer samples.

Effects of large sample loads on column lifetime in preparative-scale liquid chromatography

In preparative-scale liquid chromatography of proteins, the use of high sample concentration and large sample mass may result in irreversible adsorption to the support surface. This can change the stationary phase characteristics, reduce the capacity, shorten the column lifetime and diminish the economic viability of a particular separation method. Column recycling and regeneration can influence the throughput (mass purified per time unit) and selectivity, and affect the reproducibility. The effects of large sample loads on column lifetime and performance were evaluated for three strong anion-exchange columns: (1) a silica support with a quaternized polyethyleneimine (PEI) coating, (2) a polymeric support with an adsorbed PEI coating which also was quaternized, and (3) a polymeric support with a proprietary quaternary amine stationary phase. The column capacity for proteins was measured by frontal chromatography and monitored as a function of cycle number. The column lifetime was determined by examining chromatographic properties subsequent to the frontal chromatography. The change in protein binding capacity was then compared to the change in nitrate binding capacity. The column performance was evaluated under analytical conditions by measuring the change in resolution of standard protein mixtures.

Selective non-adsorption preparative chromatography of bovine immunoglobulin Gl

Bovine immunoglobulin Gl (IgGl) was purified from blood serum by isocratic elution through a mixed-bed ion-exchange column at low ionic strength. Selection of a mobile phase pH near the isoelectric point of IgG precluded its binding to the strong cation- and anion-exchange sorbents and allowed IgGl to be eluted isocratically. Under these conditions most of the other components in the serum sample were retained on the mixed-bed column. This approach gives excellent throughput and purity.

The role of protein structure in chromatographic behavior

Chromatographic retention is determined by a relatively small number of amino acids located in a chromatographic contact region on the surface of a polypeptide. This region is determined by the mode of separation and the amino acid distribution within the polypeptide. The contact area may be as small as a few hundred square angstroms in bioaffinity chromatography. In contrast, the contact region in ion exchange, reversed phase, hydrophobic interaction and the other nonbioaffinity separation modes is much broader, ranging from one side to the whole external surface of a polypeptide. Furthermore, structural changes that alter the chromatographic contact region will alter chromatographic properties. Thus, although immunosorbents can be very useful in purifying proteins of similar primary structure, they will be ineffective in discriminating between small, random variations within a structure. Nonbioaffinity columns complement affinity columns in probing a much larger portion of solute surface and being able to discriminate between protein variants.

Retention mechanism of lactate dehydrogenase in anion-exchange chromatography

The anion-exchange retention mechanism of lactate dehydrogenase (LDH) isoenzymes was examined under conditions where the muscle (M) subunit was not retained by the sorbent matrix. Using the stoichiometric displacement model of retention to quantitate the number (Zn) of ionic groups on the protein that interact with the sorbent matrix, it was determined that Zn for the LDH isoenzymes increases incrementally as the number of heart (H) subunits is increased up to a total of three H subunits. Both the MH3 and H4 isoenzymes have the same Zn. As the subunits in this tetrameric enzyme are arranged in a tetrahedral structure, these data indicate that steric limitations prevent any more than three subunits from interacting simultaneously with the sorbent surface. The reason why the MH3 and H4 isoenzymes could be separated is apparently that there are multiple equivalent faces in the H4 isoenzyme, and this both increases the probability and rate of adsorption and decreases the probability and rate of desorption for the H4 relative to the MH3 isoenzyme. It was concluded from these studies that the three-dimensional structure of a biopolymer will determine those surface residues which are in a position to interact with a sorbent surface and that multiple subunits or domains of a protein may act cooperatively over considerable distances in biopolymer-surface interactions.

Characterization of osmotin : a thaumatin-like protein associated with osmotic adaptation in plant cells

Cultured tobacco (Nicotiana tabacum var Wisconsin 38) cells adapted to grow under osmotic stress synthesize and accumulate a 26 kilodalton protein (osmotin) which can constitute as much as 12% of total cellular protein. In cells adapted to NaCl, osmotin occurs in two forms: an aqueous soluble form (osmotin-I) and a detergent soluble form (osmotin II) in the approximate ratio of 2:3. Osmotin-I has been purified to electrophoretic homogeneity, and osmotin-II has been purified to 90% electrophoretic homogeneity. The N-terminal amino acid sequences of osmotins I and II are identical through position 22. Osmotin-II appears to be much more resistant to proteolysis than osmotin-I. However, it cross-reacts with polyclonal antibodies raised in rabbits against osmotin-I. Osmotin strongly resembles the sweet protein thaumatin in its molecular weight, amino acid composition, N-terminal sequence, and the presence of a signal peptide on the precursor protein. Thaumatin does not cross-react with antiosmotin. An osmotin solution could not be detected as sweet at a concentration at least 100 times that of thaumatin which could be detected as sweet. Immunocytochemical detection of osmotin revealed that osmotin is concentrated in dense inclusion bodies within the vacuole. Although antiosmotin did not label organelles, cell walls, or membranes, osmotin appeared sparsely distributed in the cytoplasm.

Introduction of 5'-terminal functional groups into synthetic oligonucleotides for selective immobilization

Oligodeoxyribonucleotides terminating in a 5'-primary amine group are synthesized using solid-phase supported phosphoramidite chemistry. The 5'-terminal amine group in the deprotected oligomers is further derivatized with either succinic anhydride to give 5'-carboxylic acid or with dithiobis(succinimidylpropionate) followed by treatment with dithioerythritol to produce 5'-thiol-terminated oligonucleotides. The 5'-thiol-terminated oligonucleotides are selectively immobilized on solid supports containing either p-chloromercuribenzoate or 2,2'-dithiobis(5-nitropyridine) activated thiol groups.

Chromatography of complex protein mixtures

This review has shown that a variety of chromatographic techniques are available for fractionating proteins. Fortunately, high-quality columns of every type described in this review are commercially available. Most water-soluble proteins may be eluted from size-exclusion, hydrophobic-interaction, ion-exchange, metal chelate, and bioaffinity columns with ease. When this is the case, high recovery and retention of biological activity are the norm. The exception is reversed-phase chromatography where the organic solvents and acids used in polypeptide elution denature many proteins. When problems do occur, they are generally the result of unique structural features of the protein. Very hydrophobic proteins have presented the biggest problem in that they are difficult to solubilize, particularly with retention of biological activity. It has been found that zwitterionic and non-ionic detergents are the most suitable solubilizing agents, but urea has also been used in cases where hydrophobic interacts are not as strong. Unfortunately, there is still an element of trial-and-error in selecting the most suitable solubilizing agent. Heterogeneous glycosylation of proteins also presents a problem. Both neutral and charged monosaccharides can be incorporated into proteins through multiple steps at several sites. Thus, there is the potential in a sample for a large number of glycoprotein species which have the same polypeptide backbone and differing amounts of oligosaccharide. A problem arises when size-exclusion, ion-exchange, hydrophobic-interaction, reversed-phase and bioaffinity systems begin to discriminate between these very similar glycoprotein species. Chromatographic peaks can become very broad, due to incomplete fractionation, and the polypeptide chain of interest can be associated with multiple peaks. The separation of glycoproteins requires much more study before logical procedures can be suggested for column selection and operation. Aggregated species are another class of proteins which present occasional problems. Multimeric proteins are adsorbed to sorbents by a series of forces, among which are hydrogen bonding, hydrophobic interactions, and electrostatic forces. These forces are also responsible for the maintenance of quaternary structure in proteins. When the same forces dominate both retention of protein structure and adsorption at the sorbent surface, the quaternary structure of the protein can be disrupted during elution. Very basic proteins also present a problem in some cases. Columns with residual negative charges, such as a silica-based reversed-phase column, adsorb anionic species so strongly that they are difficult to elute.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis and immobilization of a novel acridine derivative on microparticulate silica. A study of its interactions with single-stranded oligonucleotides by high-performance liquid chromatography

A novel approach for immobilizing acridine on 5-microns silica gel is described. The acridine moiety is functionalized with a carboxylic acid group at its reactive 9-position and activated, leading to 9-acridinylpropionic acid N-hydroxysuccinimide ester. This derivative is efficiently bound to the silica matrix through a primary aliphatic amine group at the end of a fifteen-atom spacer arm. The chromatographic properties of the final stationary phases, as evaluated with d(T)10 and d(A)10 at various pH values and organic solvent concentrations, resemble those of hydrophobic weak anion exchangers. When a secondary amine group is placed close to the acridine moiety in one of the packings, enhanced binding of the oligodeoxyribonucleotides is observed that goes beyond a purely additive effect.

Poly(styrene-divinylbenzene)-based strong anion-exchange packing material for high-performance liquid chromatography of proteins

An adsorbed polyethyleneimine coating was applied to sulfonated macroporous, microparticulate poly(styrene-divinylbenzene). The chemical, physical and chromatographic properties of the resulting strong anion-exchange packing material were thoroughly characterized. The dynamic load capacity of the experimental packing was comparable to that of large-pore diameter silica. Good recoveries of protein mass and enzyme activity were achieved. The new column withstood a variety of cleaning procedures and prolonged exposure to aqueous base. The retention times on the polystyrene-based column were similar to those on a silica and a commercial, polymeric, strong anion-exchange column. Chromatographic resolution of the new packing material was equal or superior to that provided by the other two packings.

Factors contributing to intrinsic loading capacity in silica-based packing materials for preparative anion-exchange protein chromatography

Properties of the matrix and stationary phase which affect the intrinsic loading capacity of silica-based packing materials for preparative anion-exchange chromatography of proteins were investigated. Polyethyleneimine-coated controlled porosity glass beads ranging from 100 to 2000 A in pore diameter were used to evaluate the effects of pore diameter and surface area. Protein binding was found to depend on accessible, rather than total, support surface area. Consequently, wide-pore, high surface area media provide maximum intrinsic loading capacity. Increasing the number of positively charged sites on the stationary phase by increased coating or by quaternization of amines increases hemoglobin-binding capacity.

Preparation and evaluation of inorganic anion-exchange sorbents not based on silica

The use of alternate macroporous (greater than 200 A) inorganic support materials in the preparation of pellicular anion-exchange packings was explored. Alumina, magnesia, titania, and a zirconia-coated silica were chosen for comparison with silica. The stationary phase attached to the support surfaces was an adsorbed polyethyleneimine, crosslinked with 1,4-butanediol diglycidyl ether. Packing materials were characterized by static elemental analyses, chromatographic retention, static loading capacity and pH stability. Titania, alumina, and zirconyl-clad silica packings were found to be substantially more stable under alkaline conditions than silica-based materials. The data show that the stationary phase was successfully bonded in all cases and functioned in anion-exchange chromatography. When the surface area and pore diameter of these alternate materials is equivalent to silica, there is little difference in chromatographic properties.

Application of the stoichiometric displacement model of retention to anion-exchange chromatography of nucleic acids

The stoichiometric displacement model has been refined in its application to anion-exchange chromatography. The revised stoichiometric displacement model has been shown to be valid for anion-exchange chromatography with respect to all particulars of the model tested. It has been shown that the use of displacing agent activity is not a necessary condition for valid application of the stoichiometric displacement model to anion-exchange chromatography. While the cation of the displacing salt can influence anion-exchange chromatography, the data indicate that the displacing anion is of primary importance. It has been shown that solutes with three-dimensional structure have Zn value to solute charge ratios less than unity, and that the stoichiometric displacement model may be useful as a probe of solute three-dimensional structure.

Multimodal liquid chromatography columns for the separation of proteins in either the anion-exchange or hydrophobic-interaction mode

Several high-performance stationary phases suitable for protein chromatography were synthesized. Columns packed with these materials could be operated independently in either the anion-exchange or hydrophobic-interaction mode. Two approaches were used to prepare these materials. In the first method, a polyamine was adsorbed on the surface of macroporous silica and then crosslinked with a multifunctional oxirane. The hydrophobicity of the crosslinking agent and the extent of interconnection were used to modulate the electrostatic and solvophobic interactions. The second approach also utilized a crosslinked polyamine stationary phase; however, the forces of interaction were attenuated through controlled acylation of surface amines with a small anhydride molecule. The resolving ability of these columns, functioning in either mode, was comparable to commercial high-performance liquid chromatographic columns, designed to operate by a single retention mechanism. Column selectivity for proteins was completely different in each mode. Protein fractions collected from a multimodal column, operated in the anion-exchange mode, could be further purified by rechromatographing them on the same column in the hydrophobic-interaction mode. Utility of the multimodal column was demonstrated with the fractionation of several cytochromes and ferredoxins from the cyanobacterium Microcystis aeruginosa.

Solute and mobile phase contributions to retention in hydrophobic interaction chromatography of proteins

Hydrophobic interaction chromatography utilizes high salt concentrations mobile phases to induce an interaction between a weakly hydrophobic matrix and exposed hydrophobic amino acids of a native protein. Proteins with a hydrophilic exterior have shorter retention times on a hydrophobic interaction column than do proteins with more hydrophobic exteriors. To examine the effect of amino acid substitutions on protein retention, lysozyme isolated from related bird species was chromatographed on a hydrophobic interaction column at increasing ammonium sulfate concentrations. Chromatographic retention deviated only when amino acid substitutions occurred on the surface of lysozyme opposite the catalytic cleft. This area may constitute a contact surface area and extends from Residue 41 to 102 and from 75 to the alpha-helical region starting with Residue 89. Retention was analyzed by plotting log k' versus the molal concentration of ammonium sulfate. The slope did not deviate significantly for each of the bird lysozymes, indicating a similar contact surface area. However, there was significant deviation in the intercept of each of the lysozyme lines, which probably reflects the strength of the hydrophobic interaction. The intercept increased as the lysozyme became more hydrophobic. Hydrophilic amino acid substitutions affected retention as much as hydrophobic ones. The ionization state of histidine residues within the contact area between lysozyme and the column surface also influenced retention. An uncharged histidine residue increased retention, while a decrease in retention was seen with a charged histidine residue. The amino acid substitutions did not appear to affect the size of the hydrophobic contact surface area, but rather the strength of the hydrophobic interaction. The effect of salt composition on protein retention indicated that factors other than surface tension could influence retention. These factors appear to include protein hydration and specific interactions between the protein and the salt ions. Of these, the latter may or may not result in an alteration in protein structure. The magnitude of the effect of salt composition was found to be dependent upon the protein.

Synthesis of cation-exchange stationary phases using an adsorbed polymeric coating

We have prepared several silica-based cation-exchange materials that were suitable for the high-performance liquid chromatography of basic proteins. Two synthetic routes were examined. Central to both procedures was the adsorption of a low molecular weight polyamine. One method crosslinks the adsorbed polyamine with a multifunctional oxirane, which is then extensively derivatized with a monomeric cyclic anhydride. The second involves an adsorbed uncrosslinked polyethyleneimine layer which is reacted with polyacrylic anhydride, thereby crosslinking and imparting anionic character simultaneously. The resulting media prepared by either of these methods bound more than 40 mg of hemoglobin per gram of support depending on the reaction conditions. These cation-exchange stationary phases also exhibited good chromatographic performance, successfully resolving (horse heart) cytochrome c and lysozyme. Two of the more promising support materials were effectively used to isolate cytochrome c553 from a crude extract of cyanobacteria.

Synthesis of an adsorbed reversed-phase packing material for the separation of proteins and peptides

We have described the preparation and chromatographic evaluation of an adsorbed hydrophobic stationary phase suitable for reversed-phase chromatography of proteins and peptides. The synthetic procedure involves three steps: the adsorption of a polyamine to the silica surface; crosslinking of the adsorbed polyamine layer with a bis-phenyl difunctional epoxide; and the benzoylation of the remaining accessible amino groups. Performance of this chromatographic material compared favorably with SynChropak RP-8 silica (SynChrom, Linden, IN, U.S.A.) and was stable to 40% formic acid. Good separations were obtained between the components of sample mixtures containing proteins or the cyanogen bromide fragments of sperm whale myoglobin. However, in both cases, the adsorbed hydrophobic stationary phase was less retentive. Furthermore, this medium exhibited slightly different selectivity. Whereas the heme which was present in the cyanogen bromide digest of myoglobin desorbed as the second peak from the RP-8 column, it eluted last from the adsorbed stationary phase. Comparable performance, acid stability and alternate selectivity suggest that this material is an interesting alternative to organosilane reversed-phase coatings.

Stoichiometric displacement of solvent by non-polar solutes in reversed-phase liquid chromatography

This paper proposes a retention model which predicts that the displacement of non-polar solutes from a reversed-phase chromatographic column is accompanied by the adsorption of a stoichiometric number (Z) of solvent molecules. The number of solvent molecules involved in this process is a function of both solute and solvent contact surface areas. Increasing solute contact surface area would increase Z whereas increasing solvent contact surface area would decrease the Z value for a specific solute. The experimental observations presented are consistent with this model. Further predictions of the model are that (1) plots of log k' versus the inverse log of solvent concentration will be non-linear at solvent concentrations where the surface of a reversed-phase support is not fully solvated, and (2) only a portion of the total non-polar surface area of a molecule actually contacts the surface of a reversed-phase support. Non-linearity in plots of log k' versus the inverse log of solvent concentration was in fact observed at solvent concentrations where solvation of the reversed-phase support is incomplete.

High-performance anion-exchange chromatography of oligonucleotides

Several types of high-performance silica-based supports have been found to be effective in the separation of polynucleotides. The principal difference in these materials is the type of bonded phase and the method by which it is attached to the silica support. One approach is the coupling of stationary-phase groups to the surface through siloxane bonding. This technique is simple and produces a material of high capacity and resolution, but it suffers from poor bonded-phase stability. An alternative approach is the adsorption of low-molecular-weight polyethylene imines (PEI) that are crosslinked into a surface film. The stationary phase is held in place by adsorption of the film at multiple sites. A previous report on this material showed the resolution of oligonucleotides containing up to 30 bases. This paper reports further optimization of the PEI bonding chemistry in the preparation of HP-IEC columns for oligonucleotides and tRNA species. Quaternization of the ion-exchange matrix was found to increase resolution of oligonucleotides from 30 to 50 bases. The same support was found to be capable of resolving multiple tRNA species. Separations were achieved on small (0.42 X 5 cm) columns, using a 60- to 120-min ammonium sulfate gradient. The initial solvent was 15% acetonitrile in 0.05 M potassium phosphate (pH 5.9). The addition of 1 M ammonium sulfate to the initial solvent was used to prepare the final solvent.

Stationary phase contributions to retention in high-performance anion-exchange protein chromatography: ligand density and mixed mode effects

Several anion-exchange stationary phases (based on polyethyleneimine-coated silica) were synthesized so as to vary in ligand density and hydrophobicity. These materials were first examined for hemoglobin-binding capacity and then evaluated chromatographically. Protein binding, retention and resolution increased concomitantly with ligand density. Ferritin (molecular weight 440,000) could not be eluted from the more highly-charged surfaces, but was desorbed from a low ligand density support. The above parameters also varied with the hydrophobic character of the stationary phase. Retention and resolution increased as more hydrophobic moieties were added. Data from a non-ionic hemoglobin-binding assay correlated reasonably well with anticipated matrix hydrophobicities. Possible explanations and applications of the observed phenomena are discussed.

Comparison of hydrophobic-interaction and reversed-phase chromatography of proteins

The variable hydrophobic nature of proteins allows their separation through differential hydrophobic surface interactions. From these observations two modes of protein chromatography have been developed, hydrophobic-interaction chromatography (HIC) and reversed-phase chromatography (RPC). Selectivity of the HIC column can be easily manipulated by changing mobile phase variables. Protein retention was increased by decreasing the pH from neutrality or by using a salt with a greater "salting-out" ability. In addition, selectivity can be altered through chemical modification of the matrix surface. Protein retention and resolution decreased concomitantly with matrix ligand density. There were several major differences in HIC and RPC selectivity. Hydrophilic proteins such as cytochrome c and myoglobin were weakly retained on the HIC column but strongly retained on the RPC column. In contrast, a hydrophobic protein such as beta-glucosidase was strongly retained on the HIC column and only weakly retained on the RPC column. Other proteins were retained equally by RPC and HIC columns. Load capacity on the HIC column was determined by plotting resolution as a function of protein load. Resolution decreased significantly after 7.5 mg of total protein had been loaded onto the column per cm3 of column material. Samples of lactic dehydrogenase and alpha-chymotrypsin ranging in size from 10-200 micrograms were recovered from an HIC column with greater than 86% enzymatic activity in all cases. The recovery of enzymatic activity of alpha-chymotrypsin ranged from 55-91%, while none of the activity of beta-glucosidase was recovered from the RPC column.